I just replaced Lua with LuaJIT for my project and I got the error saying
Use of undeclared identifier 'lua_len'
How can I change lua_len so it is compatible with Lua 5.1 and LuaJIT?
Here's my code that uses lua_len from the SWIG binding. (In case it helps)
%typemap(in) (int argc, t_atom *argv)
{
if (!lua_istable(L, $input)) {
SWIG_exception(SWIG_RuntimeError, "argument mismatch: table expected");
}
lua_len(L, $input);
$1 = lua_tointeger(L, -1);
if (!$1) {
SWIG_exception(SWIG_RuntimeError, "table is empty");
}
$2 = (t_atom *)getbytes($1 * sizeof(t_atom));
for (int i=0; i<$1; ++i) {
lua_pushinteger(L, i+1);
lua_gettable(L, $input);
if (lua_isnumber(L, -1)) {
$2[i].a_type = A_FLOAT;
$2[i].a_w.w_float = lua_tonumber(L, -1);
}
else if (lua_isstring(L, -1)) {
$2[i].a_type = A_SYMBOL;
$2[i].a_w.w_symbol = gensym(lua_tostring(L, -1));
}
else {
SWIG_exception(SWIG_RuntimeError, "unhandled argument type");
}
}
}
You can backport lua_len to Lua 5.1 by using lua-compat-5.3. If you don't want all of that, you can just use part of it by inlining it into your interface file. In case of lua_len you need
%{
static void lua_len (lua_State *L, int i) {
switch (lua_type(L, i)) {
case LUA_TSTRING:
lua_pushnumber(L, (lua_Number)lua_objlen(L, i));
break;
case LUA_TTABLE:
if (!luaL_callmeta(L, i, "__len"))
lua_pushnumber(L, (lua_Number)lua_objlen(L, i));
break;
case LUA_TUSERDATA:
if (luaL_callmeta(L, i, "__len"))
break;
/* FALLTHROUGH */
default:
luaL_error(L, "attempt to get length of a %s value",
lua_typename(L, lua_type(L, i)));
}
}
%}
Related
I'm trying to call lua_yield inside a debug hook, and get this error in my output. I'm wanting to yield after a certain number of instructions have been processed and was hoping this was the way to do it.
I'm writing this using some Python ctypes bindings.
yielding
b'test.lua:1: attempt to yield across C-call boundary'
I assumed this should work since I'm using LuaJIT and it has a fully resumable VM.
#lua_Hook
def l_dbg_count(L: lua_State_p, ar: ctypes.POINTER(lua_Debug)):
if ar.contents.event == EventCode.HookCount:
print("yielding")
lua_yield(L, 0)
#main method
def main():
...
lua_sethook(L, l_dbg_count, DebugEventMask.Count, 1)
luaL_loadfile(L, b"test.lua")
ret = lua_pcall(L, 0, 0, 0)
while True:
if ret != LuaError.Ok and ret != LuaError.Yield:
print(lua_tostring(L, -1))
break
elif ret == LuaError.Yield:
print("resuming")
ret = lua_resume(L, None, 0)
lua_close(L)
I first must push a new thread using lua_newthread, then calling luaL_loadfile and instead of lua_pcall, calling lua_resume.
I rewrote this in C to check if there was possible stack unwinding issues from Lua to Python.
void l_dbg_count(lua_State *L, lua_Debug *ar) {
if(ar->event == LUA_HOOKCOUNT) {
printf("yielding\n");
lua_yield(L, 0);
}
}
...
int main(int argc, char **argv) {
lua_State *L = luaL_newstate();
luaL_openlibs(L);
lua_sethook(L, l_dbg_count, LUA_MASKCOUNT, 5);
lua_State *L_t = lua_newthread(L);
luaL_loadfile(L_t, "test.lua");
int ret = lua_resume(L_t, 0);
while(true) {
if(ret != 0 && ret != LUA_YIELD) {
fprintf(stderr, "%s", lua_tostring(L_t, -1));
break;
} else if(ret == LUA_YIELD) {
printf("resuming\n");
ret = lua_resume(L_t, 0);
} else {
break;
}
}
lua_close(L);
return EXIT_SUCCESS;
}
This however does break the coroutine library from working it seems, so currently looking into a possible fix for that.
The code below does compile, but it doesn't run as it should.
I'm not sure what am I doing wrong, so would someone be willing to tell me what I did wrong and what I should have done better.
What do I need to change to make it run properly?
#include<stdio.h>
#include<stdlib.h>
typedef struct sub_Node
{
int value;
struct sub_Node *next;
}sub_Node;
typedef struct Node
{
char *name;
struct Node *next;
struct sub_Node *sub_start;
}Node;
Node *start;
void add_player(char *name)
{
Node *temp;
temp = (Node *)malloc(sizeof(Node));
temp->next = start;
temp->name = name;
temp->sub_start = (sub_Node *)malloc(sizeof(sub_Node));
temp->sub_start->next = NULL;
temp->sub_start->value = -1;
start = temp;
}
void initialize()
{
char *p;
p = "\0";
add_player(p);
}
void remove_player(char *name)
{
Node *p;
for(p = start; p!= NULL; p = p->next)
if(p->name == name)
{
p->name = p->next->name;
p->next = p->next->next;
}
}
sub_Node* add_descending(sub_Node* sub_start, int piece_value)
{
sub_Node *temp, *prev, *next;
temp = (sub_Node *)malloc(sizeof(sub_Node));
temp->value = piece_value;
temp->next = NULL;
prev = NULL;
next = sub_start;
while(next && next->value >= piece_value)
{
prev = next;
next = next->next;
}
if(!next)
{
prev->next = temp;
}
else
{
if(prev)
{
temp->next = prev->next;
prev->next = temp;
}
else
{
temp->next = sub_start;
sub_start = temp;
}
}
return sub_start;
}
void add_piece(char *name, int piece_value)
{
Node *p;
int c;
for(p = start; p!=NULL; p = p->next)
if(p->name == name)
p->sub_start = add_descending(p->sub_start, piece_value);
}
void print_pieces(char *name)
{
Node *p;
sub_Node *q;
for(p = start; p!=NULL; p = p->next)
if(p->name == name)
{
printf("The values of the owned pieces are:");
for(q = p->sub_start; q->value != -1; q = q->next)
printf(" %d", q->value);
}
}
int lose_piece(char *name)
{
Node *p;
sub_Node *q;
int aux;
for(p = start; p!=NULL; p = p->next)
if(p->name == name)
{
for(q = p->sub_start; q->next->value != -1; q = q->next) {}
aux = q->value;
q->value = q->next->value;
q->next = q->next->next;
return aux;
}
}
void print_players()
{
Node *p;
printf("The players are: ");
for(p = start; p->name != "\0"; p = p->next)
printf("%s ", p->name);
printf("\n");
}
int main()
{
initialize();
int y, value;
char name[20];
printf("Insert a digit to execute the desired task:\n"
"<0> end the program\n"
"<1> add a player, who doesn't own any piece yet\n"
"<2> remove a player and all his pieces\n"
"<3> print the name of all the players\n"
"<4> a player gets a piece\n"
"<5> a player loses the piece with the lowest value out of the ones that he has\n"
"<6> prints the pieces of a player in a descending order by value\n\n");
do
{
printf("digit: ");
scanf("%d", &y);
switch(y)
{
case 1:
printf("Insert the player's name: ");
scanf("%s", name);
add_player(name);
break;
case 2:
printf("Insert the player's name: ");
scanf("%s", name);
remove_player(name);
break;
case 3:
print_players();
break;
case 4:
printf("Insert the player's name: ");
scanf("%s", name);
printf("Insert the value of the piece: ");
scanf("%d", value);
add_piece(name, value);
break;
case 5:
printf("Insert the player's name: ");
scanf("%s", name);
printf("\nThe player loses the piece: %d\n", lose_piece(name));
break;
case 6:
printf("Insert the player's name: ");
scanf("%s", name);
print_pieces(name);
}
} while(y != 0);
return 0;
}
your two main problems where this scanf("%d", value); value should be passed by reference like this scanf("%d", &value); and the second is string comparison in c as in your code p->name != "\0" and if(p->name == name) this is wrong because actually you are making comparison between addresses of strings (where it resides in memory) not strings values. to compare strings in c you have to use strcmp and families.
Actually 3 main problems. for setting string values as you did in temp->name = name; is little bit more complicated than that. because you are assigning to temp->name a string from the stack that is volatile (the stack will be more likely invalid soon you return from the function) . in your case you have to alloc a new string by using malloc (and friends) or just by using strdup.
here is as a bonus a slightly rewrite of your program, you will find many advises and is a good starting point for how to structure your code for an easy maintenance.
still want to advise you to change members and variables to more declarative names as in sub_start and sub_Node can be PieceNode and pieces respectively.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct sub_Node
{
int value;
struct sub_Node *next;
}sub_Node;
typedef struct Node
{
char *name;
struct Node *next;
struct Node *prev; // this to make life easyer
struct sub_Node *sub_start;
}Node;
Node *start = NULL;
Node *find_player(char *name){
Node *tmp = start;
while( tmp ){
if(strcmp(tmp->name,name) == 0 )
break;
tmp = tmp->next;
}
return tmp;
}
// int to return Error Code
//
int add_player(char *name)
{
Node *temp;
if( find_player(name)) {
printf("player %s already exists\n", name);
return 1;
}
// do not cast malloc
temp = malloc(sizeof(Node));
if( !temp ){
printf ("not enough memory\n");
return 2;
}
temp->name = strdup ( name); // here was your error
temp->sub_start = NULL; // keep it simple
temp->prev = NULL;
temp->next = start;
if(start)
start->prev = temp;
start = temp;
return 0; // no error
}
void DestroyPieces(sub_Node* piece){
if( piece ) {
DestroyPieces( piece->next );
free( piece );
}
}
// as usual use int to return error code
int remove_player(char *name)
{
Node *player = find_player(name);
if ( !player ){
return 1; // player not found
}
if ( player->next ){
player->next->prev = player->prev;
}
if ( player->prev ){
player->prev->next = player->next;
}
DestroyPieces(player->sub_start);
free(player->name);
free(player);
return 0; // success
}
sub_Node* new_piece(int value){
sub_Node *temp = malloc( sizeof(sub_Node) );
if(temp){
temp->value = value;
temp->next = NULL;
}
return temp;
}
// int to return error code
// pass sub_start as pointer to pointer, as it might be updated
int add_descending(sub_Node** psub_start, int piece_value)
{
sub_Node *piece, *current, *prev = NULL;
if( !psub_start){
return 5; // this should not happen
}
current = *psub_start;
piece = new_piece( piece_value );
if( !piece ) return 1; // no mem
if(!current){
// this is the first and only one
*psub_start = piece;
return 0; // OK
}
while(current && current->value >= piece_value)
{
prev = current;
current = current->next;
}
if( prev )
prev->next = piece;
piece->next = current;
if( current == *psub_start ){
*psub_start = piece;
}
return 0 ; // OK
}
void add_piece(Node * player, int piece_value)
{
if ( !player) {
return ;
}
if(add_descending (&(player->sub_start), piece_value) == 0 )
return ; //OK
printf("an error occured while adding a piece (%d) to player '%s'\n",piece_value,player->name);
}
void print_pieces(Node *player)
{
sub_Node *q;
if( !player ){
return;
}
if( !player->sub_start ){
printf("Player '%s' has no pieces\n",player->name);
return;
}
printf("The values of the owned pieces are:");
for(q = player->sub_start; q != NULL; q = q->next)
printf(" %d", q->value);
printf("\n");
}
void lose_piece(Node *player)
{
if( !player ){
return;
}
sub_Node *q, *prev = NULL;
int aux;
if( !player->sub_start ){
printf("Player '%s' has no pieces\n",player->name);
return;
}
// i think you want drop the last one
for(q = player->sub_start; q->next != NULL ;prev = q, q = q->next) {
;
}
if(prev)
prev->next = NULL;
else
player->sub_start = NULL;
aux = q->value;
free(q);
printf("\nThe player loses the piece: %d\n", aux);
return;
}
void print_players()
{
Node *p;
if( !start ){
printf("there are no players, try to add some\n");
return;
}
printf("The players are: ");
for(p = start; p != NULL; p = p->next)
printf("%s ", p->name);
printf("\n");
}
void print_menu(void){
printf("Insert a digit to execute the desired task:\n"
"<0> end the program\n"
"<1> add a player, who doesn't own any piece yet\n"
"<2> remove a player and all his pieces\n"
"<3> print the name of all the players\n"
"<4> a player gets a piece\n"
"<5> a player loses the piece with the lowest value out of the ones that he has\n"
"<6> prints the pieces of a player in a descending order by value\n\n");
}
Node * get_player(char *name){
Node *player = find_player(name);
if(!player)
printf("Player '%s' do not exists\n",name);
return player;
}
int main()
{
// initialize(); no more needed
int y, value;
char name[20];
Node *player;
print_menu();
do
{
printf("digit: ");
scanf("%d", &y);
switch(y)
{
case 1:
printf("Insert the player's name: ");
scanf("%s", name);
add_player(name);
break;
case 2:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
if( player )
break;
case 3:
print_players();
break;
case 4:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
if( player ){
printf("Insert the value of the piece: ");
scanf("%d", &value);
add_piece(player, value);
}
break;
case 5:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
lose_piece(player);
break;
case 6:
printf("Insert the player's name: ");
scanf("%s", name);
player = get_player(name);
print_pieces(player);
}
} while(y != 0);
return 0;
}
Need some help with reading in lines of data from a text file using the fgets and string tokenization commands, which will then be used to create a linked list. I've followed some examples I've found on Stack Overflow and other tutorial websites, but still cannot get the read function below to work properly in my program, it just causes it to crash. The data file has lines like this:
Zucchini, Squash, pound, 2.19, 45
Yellow, Squash, pound, 1.79, 15
Based on everything I've read, I believe I have the necessary code, but obviously I'm missing something. Also, I commented out one of the fields (the one for float price) as I'm not sure what to use to copy the float value from the data, as I cannot treat it as a string (the integer value right below it seems to let me get away with it in my compiler).
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// Struct for linked list node
struct produceItem
{
char produce[20];
char type[20];
char soldBy[20];
float price;
int quantityInStock;
struct produceItem *next;
};
// Function to read in data from file to
void read(struct produceItem **head)
{
struct produceItem *temp = NULL;
struct produceItem *right = NULL;
//char ch[3];
char line[50];
char *value;
FILE *data = fopen("RecitationFiveInput.txt", "r");
printf("Trying to open file RecitationFiveInput.txt\n");
if (data == NULL)
{
printf("Could not open file RecitationFiveInput.txt\n");
}
else
{
while(fgets(line, sizeof(line), data))
{
value = strtok(line, ", ");
strcpy(temp->produce, strdup(value));
value = strtok(NULL, ", ");
strcpy(temp->type, strdup(value));
value = strtok(NULL, ", ");
strcpy(temp->soldBy, strdup(value));
//value = strtok(NULL, ", ");
//strcpy(temp->price, strdup(value));
value = strtok(NULL, " \n");
strcpy(temp->quantityInStock, strdup(value));
temp->next = NULL;
if (*head == NULL)
{
*head = temp;
}
else
{
right = *head;
while(right->next != NULL)
{
right = right->next;
}
right->next = temp;
}
}
printf("Successfully opened file RecitationFiveInput.txt\n");
}
fclose(data);
return;
}
// Function to display the nodes of the linked list that contains the data from the data file
void display(struct produceItem *head)
{
int value = 1;
struct produceItem *temp = NULL;
temp = head;
printf("=============================================================================\n");
printf(" Item # Produce Type Sold By Price In Stock\n");
printf("=============================================================================\n");
if(temp == NULL)
{
return;
}
else
{
while(temp != NULL)
{
printf(" %d %s %s %s %lf %d\n", value, temp->produce, temp->type, temp->soldBy, temp->price, temp->quantityInStock);
value++;
temp = temp->next;
if(temp == NULL)
{
break;
}
}
}
return;
}
//Main function
int main()
{
int input = 0;
struct produceItem *head = NULL;
while(1)
{
printf("\nList Operations\n");
printf("=================\n");
printf("1. Stock Produce Department\n");
printf("2. Display Produce Inventory\n");
printf("3. Reverse Order of Produce Inventory\n");
printf("4. Export Produce Inventory\n");
printf("5. Exit Program\n");
printf("Enter your choice: ");
if(scanf("%d", &input) <= 0)
{
printf("Enter only an integer.\n");
exit(0);
}
else
{
switch(input)
{
case 1:
read(&head);
break;
case 2:
display(head);
break;
case 3:
//function
break;
case 4:
//function
break;
case 5:
printf("You have exited the program, Goodbye!\n");
return 0;
break;
default:
printf("Invalid option.\n");
}
}
}
return 0;
}
Never mind everyone, found the issue. The crashes were due to me not allocating memory for the temp pointer in the read me function.
I just want to resume the func coroutine twice, yield if n==0, and return if n==1 , but it core dumps, what't wrong with it?
the "hello world" should always be left in LL's stack, I can't figure out what is wrong.
[liangdong#cq01-clientbe-code00.vm.baidu.com lua]$ ./main
func_top=1 top=hello world
first_top=1 top_string=hello world
Segmentation fault (core dumped)
[liangdong#cq01-clientbe-code00.vm.baidu.com lua]$ cat main.c
#include "lua.h"
#include "lualib.h"
#include "lauxlib.h"
int n = 0;
int func(lua_State *L) {
printf("func_top=%d top=%s\n", lua_gettop(L), lua_tostring(L, -1));
if (!n) {
++ n;
return lua_yield(L, 1);
} else {
return 1;
}
}
int main(int argc, char* const argv[]) {
lua_State *L = luaL_newstate();
/* init lua library */
lua_pushcfunction(L, luaopen_base);
if (lua_pcall(L, 0, 0, 0) != 0) {
return 1;
}
lua_pushcfunction(L, luaopen_package);
if (lua_pcall(L, 0, 0, 0 ) != 0) {
return 2;
}
/* create the coroutine */
lua_State *LL = lua_newthread(L);
lua_pushcfunction(LL, func);
lua_pushstring(LL, "hello world");
/* first time resume */
if (lua_resume(LL, 1) == LUA_YIELD) {
printf("first_top=%d top_string=%s\n", lua_gettop(LL), lua_tostring(LL, -1));
/* twice resume */
if (lua_resume(LL, 1) == 0) {
printf("second_top=%d top_string=%s\n", lua_gettop(LL), lua_tostring(LL, -1));
}
}
lua_close(L);
return 0;
}
it core dumps in lua5.1, but works well in lua5.2 if change lua_resume(LL, 1) to lua_resume(LL, NULL, 1).
EDIT: I was actually totally wrong.
You cannot resume a C function.
I'm creating a Brainfuck parser (in a BASIC dialect) ultimately to create an interpreter but i've realise it's not as straight forward as i first thought. My problem is that i need a way to accurately parse the matching loop operators within a Brainfuck program. This is an example program:
,>,>++++++++[<------<------>>-]
<<[>[>+>+<<-]>>[<<+>>-]<<<-]
>>>++++++[<++++++++>-],<.>.
'[' = start of loop
']' = end of loop
I need to record the start and end point of each matching loop operator so i can jump around the source as needed. Some loops are alone, some are nested.
What would be the best way to parse this? I was thinking maybe move through the source file creating a 2D array (or such like) recording the start and end positions of each matching operator, but this seems like a lot of 'to'ing and fro'ing' through the source. Is this the best way to do it?
More info: Brainfuck homepage
EDIT: Sample code in any language greatly appreciated.
Have you considered using a Stack data structure to record "jump points" (i.e. the location of the instruction pointer).
So basically, every time you encounter a "[" you push the current location of the instruction pointer on this stack. Whenever you encounter a "]" you reset the instruction pointer to the value that's currently on the top of the stack. When a loop is complete, you pop it off the stack.
Here is an example in C++ with 100 memory cells. The code handles nested loops recursively and although it is not refined it should illustrate the concepts..
char cells[100] = {0}; // define 100 memory cells
char* cell = cells; // set memory pointer to first cell
char* ip = 0; // define variable used as "instruction pointer"
void interpret(static char* program, int* stack, int sp)
{
int tmp;
if(ip == 0) // if the instruction pointer hasn't been initialized
ip = program; // now would be a good time
while(*ip) // this runs for as long as there is valid brainF**k 'code'
{
if(*ip == ',')
*cell = getch();
else if(*ip == '.')
putch(*cell);
else if(*ip == '>')
cell++;
else if(*ip == '<')
cell--;
else if(*ip == '+')
*cell = *cell + 1;
else if(*ip == '-')
*cell = *cell - 1;
else if(*ip == '[')
{
stack[sp+1] = ip - program;
*ip++;
while(*cell != 0)
{
interpret(program, stack, sp + 1);
}
tmp = sp + 1;
while((tmp >= (sp + 1)) || *ip != ']')
{
*ip++;
if(*ip == '[')
stack[++tmp] = ip - program;
else if(*ip == ']')
tmp--;
}
}
else if(*ip == ']')
{
ip = program + stack[sp] + 1;
break;
}
*ip++; // advance instruction
}
}
int _tmain(int argc, _TCHAR* argv[])
{
int stack[100] = {0}; // use a stack of 100 levels, modeled using a simple array
interpret(",>,>++++++++[<------<------>>-]<<[>[>+>+<<-]>>[<<+>>-]<<<-]>>>++++++[<++++++++>-],<.>.", stack, 0);
return 0;
}
EDIT
I just went over the code again and I realized there was a bug in the while loop that would 'skip' parsed loops if the value of the pointer is 0. This is where I made the change:
while((tmp >= (sp + 1)) || *ip != ']') // the bug was tmp > (sp + 1)
{
ip++;
if(*ip == '[')
stack[++tmp] = ip - program;
else if(*ip == ']')
tmp--;
}
Below is an implementation of the same parser but without using recursion:
char cells[100] = {0};
void interpret(static char* program)
{
int cnt; // cnt is a counter that is going to be used
// only when parsing 0-loops
int stack[100] = {0}; // create a stack, 100 levels deep - modeled
// using a simple array - and initialized to 0
int sp = 0; // sp is going to be used as a 'stack pointer'
char* ip = program; // ip is going to be used as instruction pointer
// and it is initialized at the beginning or program
char* cell = cells; // cell is the pointer to the 'current' memory cell
// and as such, it is initialized to the first
// memory cell
while(*ip) // as long as ip point to 'valid code' keep going
{
if(*ip == ',')
*cell = getch();
else if(*ip == '.')
putch(*cell);
else if(*ip == '>')
cell++;
else if(*ip == '<')
cell--;
else if(*ip == '+')
*cell = *cell + 1;
else if(*ip == '-')
*cell = *cell - 1;
else if(*ip == '[')
{
if(stack[sp] != ip - program)
stack[++sp] = ip - program;
*ip++;
if(*cell != 0)
continue;
else
{
cnt = 1;
while((cnt > 0) || *ip != ']')
{
*ip++;
if(*ip == '[')
cnt++;
else if(*ip == ']')
cnt--;
}
sp--;
}
}else if(*ip == ']')
{
ip = program + stack[sp];
continue;
}
*ip++;
}
}
int _tmain(int argc, _TCHAR* argv[])
{
// define our program code here..
char *prg = ",>++++++[<-------->-],[<+>-]<.";
interpret(prg);
return 0;
}
Interesting enough, just a couple days ago, I was writing a brainf*ck interpreter in Java.
One of the issues I was having was that the explanation of the commands at the official page was insufficient, and did not mention the part about nested loops. The Wikipedia page on Brainf*ck has a Commands subsection which describes the correct behavior.
Basically to summarize the problem, the official page says when an instruction is a [ and the current memory location is 0, then jump to the next ]. The correct behavior is to jump to the corresponding ], not the next one.
One way to achieve this behavior is to keep track of the level of nesting. I ended up implementing this by having a counter which kept track of the nesting level.
The following is part of the interpreter's main loop:
do {
if (inst[pc] == '>') { ... }
else if (inst[pc] == '<') { ... }
else if (inst[pc] == '+') { ... }
else if (inst[pc] == '-') { ... }
else if (inst[pc] == '.') { ... }
else if (inst[pc] == ',') { ... }
else if (inst[pc] == '[') {
if (memory[p] == 0) {
int nesting = 0;
while (true) {
++pc;
if (inst[pc] == '[') {
++nesting;
continue;
} else if (nesting > 0 && inst[pc] == ']') {
--nesting;
continue;
} else if (inst[pc] == ']' && nesting == 0) {
break;
}
}
}
}
else if (inst[pc] == ']') {
if (memory[p] != 0) {
int nesting = 0;
while (true) {
--pc;
if (inst[pc] == ']') {
++nesting;
continue;
} else if (nesting > 0 && inst[pc] == '[') {
--nesting;
continue;
} else if (inst[pc] == '[' && nesting == 0) {
break;
}
}
}
}
} while (++pc < inst.length);
Here is the legend for the variable names:
memory -- the memory cells for the data.
p -- pointer to the current memory cell location.
inst -- an array holding the instructions.
pc -- program counter; points to the current instruction.
nesting -- level of the nesting of the current loop. nesting of 0 means that the current location is not in a nested loop.
Basically, when a loop opening [ is encountered, the current memory location is checked to see if the value is 0. If that is the case, a while loop is entered to jump to the corresponding ].
The way the nesting is handled is as follows:
If an [ is encountered while seeking for the corresponding loop closing ], then the nesting variable is incremented by 1 in order to indicate that we have entered a nested loop.
If an ] is encountered, and:
a. If the nesting variable is greater than 0, then the nesting variable is decremented by 1 to indicate that we've left a nested loop.
b. If the nesting variable is 0, then we know that the end of the loop has been encountered, so seeking the end of the loop in the while loop is terminated by executing a break statement.
Now, the next part is to handle the closing of the loop by ]. Similar to the opening of the loop, it will use the nesting counter in order to determine the current nesting level of the loop, and try to find the corresponding loop opening [.
This method may not be the most elegant way to do things, but it seems like it is resource-friendly because it only requires one extra variable to use as a counter for the current nesting level.
(Of course, "resource-friendly" is ignoring the fact that this interpreter was written in Java -- I just wanted to write some quick code and Java just happened to be what I wrote it in.)
The canonical method for parsing a context-free grammar is to use a stack. Anything else and you're working too hard and risking correctness.
You may want to use a parser generator like cup or yacc, as a lot of the dirty work is done for you, but with a language as simple as BF, it may be overkill.
Each time you find a '[', push the current position (or another "marker" token or a "context") on a stack. When you come accross a ']', you're at the end of the loop, and you can pop the marker token from the stack.
Since in BF the '[' already checks for a condition and may need jump past the ']', you may want to have a flag indicating that instructions shall be skipped in the current loop context.
Python 3.0 example of the stack algorithm described by the other posters:
program = """
,>,>++++++++[<------<------>>-]
<<[>[>+>+<<-]>>[<<+>>-]<<<-]
>>>++++++[<++++++++>-],<.>.
"""
def matching_brackets(program):
stack = []
for p, c in enumerate(program, start=1):
if c == '[':
stack.append(p)
elif c == ']':
yield (stack.pop(), p)
print(list(matching_brackets(''.join(program.split()))))
(Well, to be honest, this only finds matching brackets. I don't know brainf*ck, so what to do next, I have no idea.)
And here's the same code I gave as an example earlier in C++, but ported to VB.NET. I decided to post it here since Gary mentioned he was trying to write his parser in a BASIC dialect.
Public cells(100) As Byte
Sub interpret(ByVal prog As String)
Dim program() As Char
program = prog.ToCharArray() ' convert the input program into a Char array
Dim cnt As Integer = 0 ' a counter to be used when skipping over 0-loops
Dim stack(100) As Integer ' a simple array to be used as stack
Dim sp As Integer = 0 ' stack pointer (current stack level)
Dim ip As Integer = 0 ' Instruction pointer (index of current instruction)
Dim cell As Integer = 0 ' index of current memory
While (ip < program.Length) ' loop over the program
If (program(ip) = ",") Then
cells(cell) = CByte(AscW(Console.ReadKey().KeyChar))
ElseIf (program(ip) = ".") Then
Console.Write("{0}", Chr(cells(cell)))
ElseIf (program(ip) = ">") Then
cell = cell + 1
ElseIf (program(ip) = "<") Then
cell = cell - 1
ElseIf (program(ip) = "+") Then
cells(cell) = cells(cell) + 1
ElseIf (program(ip) = "-") Then
cells(cell) = cells(cell) - 1
ElseIf (program(ip) = "[") Then
If (stack(sp) <> ip) Then
sp = sp + 1
stack(sp) = ip
End If
ip = ip + 1
If (cells(cell) <> 0) Then
Continue While
Else
cnt = 1
While ((cnt > 0) Or (program(ip) <> "]"))
ip = ip + 1
If (program(ip) = "[") Then
cnt = cnt + 1
ElseIf (program(ip) = "]") Then
cnt = cnt - 1
End If
End While
sp = sp - 1
End If
ElseIf (program(ip) = "]") Then
ip = stack(sp)
Continue While
End If
ip = ip + 1
End While
End Sub
Sub Main()
' invoke the interpreter
interpret(",>++++++[<-------->-],[<+>-]<.")
End Sub
I don't have sample code, but.
I might try using a stack, along with an algorithm like this:
(executing instruction stream)
Encounter a [
If the pointer == 0, then keep reading until you encounter the ']', and don't execute any instructions until you reach it.. Goto step 1.
If the pointer !=0, then push that position onto a stack.
Continue executing instructions
If you encounter a ]
If pointer==0, pop the [ off of the stack, and proceed (goto step 1)
If pointer != 0, peek at the top of the stack, and go to that position. (goto step 5)
This question is a bit old, but I wanted to say that the answers here helped me decide the route to take when writing my own Brainf**k interpreter. Here's the final product:
#include <stdio.h>
char *S[9999], P[9999], T[9999],
**s=S, *p=P, *t=T, c, x;
int main() {
fread(p, 1, 9999, stdin);
for (; c=*p; ++p) {
if (c == ']') {
if (!x)
if (*t) p = *(s-1);
else --s;
else --x;
} else if (!x) {
if (c == '[')
if (*t) *(s++) = p;
else ++x;
}
if (c == '<') t--;
if (c == '>') t++;
if (c == '+') ++*t;
if (c == '-') --*t;
if (c == ',') *t = getchar();
if (c == '.') putchar(*t);
}
}
}
package interpreter;
import java.awt.event.ActionListener;
import javax.swing.JTextPane;
public class Brainfuck {
final int tapeSize = 0xFFFF;
int tapePointer = 0;
int[] tape = new int[tapeSize];
int inputCounter = 0;
ActionListener onUpdateTape;
public Brainfuck(byte[] input, String code, boolean debugger,
JTextPane output, ActionListener onUpdate) {
onUpdateTape = onUpdate;
if (debugger) {
debuggerBF(input, code, output);
} else {
cleanBF(input, code, output);
}
}
private void debuggerBF(byte[] input, String code, JTextPane output) {
for (int i = 0; i < code.length(); i++) {
onUpdateTape.actionPerformed(null);
switch (code.charAt(i)) {
case '+': {
tape[tapePointer]++;
break;
}
case '-': {
tape[tapePointer]--;
break;
}
case '<': {
tapePointer--;
break;
}
case '>': {
tapePointer++;
break;
}
case '[': {
if (tape[tapePointer] == 0) {
int nesting = 0;
while (true) {
++i;
if (code.charAt(i) == '[') {
++nesting;
continue;
} else if (nesting > 0 && code.charAt(i) == ']') {
--nesting;
continue;
} else if (code.charAt(i) == ']' && nesting == 0) {
break;
}
}
}
break;
}
case ']': {
if (tape[tapePointer] != 0) {
int nesting = 0;
while (true) {
--i;
if (code.charAt(i) == ']') {
++nesting;
continue;
} else if (nesting > 0 && code.charAt(i) == '[') {
--nesting;
continue;
} else if (code.charAt(i) == '[' && nesting == 0) {
break;
}
}
}
break;
}
case '.': {
output.setText(output.getText() + (char) (tape[tapePointer]));
break;
}
case ',': {
tape[tapePointer] = input[inputCounter];
inputCounter++;
break;
}
}
}
}
private void cleanBF(byte[] input, String code, JTextPane output) {
for (int i = 0; i < code.length(); i++) {
onUpdateTape.actionPerformed(null);
switch (code.charAt(i)) {
case '+':{
tape[tapePointer]++;
break;
}
case '-':{
tape[tapePointer]--;
break;
}
case '<':{
tapePointer--;
break;
}
case '>':{
tapePointer++;
break;
}
case '[': {
if (tape[tapePointer] == 0) {
int nesting = 0;
while (true) {
++i;
if (code.charAt(i) == '[') {
++nesting;
continue;
} else if (nesting > 0 && code.charAt(i) == ']') {
--nesting;
continue;
} else if (code.charAt(i) == ']' && nesting == 0) {
break;
}
}
}
break;
}
case ']': {
if (tape[tapePointer] != 0) {
int nesting = 0;
while (true) {
--i;
if (code.charAt(i) == ']') {
++nesting;
continue;
} else if (nesting > 0 && code.charAt(i) == '[') {
--nesting;
continue;
} else if (code.charAt(i) == '[' && nesting == 0) {
break;
}
}
}
break;
}
case '.':{
output.setText(output.getText()+(char)(tape[tapePointer]));
break;
}
case ',':{
tape[tapePointer] = input[inputCounter];
inputCounter++;
break;
}
}
}
}
public int[] getTape() {
return tape;
}
public void setTape(int[] tape) {
this.tape = tape;
}
public void editTapeValue(int counter, int value) {
this.tape[counter] = value;
}
}
This should work. You need to modify it somewhat.
That is actually standard example how brainfuck interpreter works. I modified it to use in my app, brackets are handled there:
case '[': {
if (tape[tapePointer] == 0) {
int nesting = 0;
while (true) {
++i;
if (code.charAt(i) == '[') {
++nesting;
continue;
}
else if (nesting > 0 && code.charAt(i) == ']') {
--nesting;
continue;
}
else if (code.charAt(i) == ']' && nesting == 0) {
break;
}
}
}
break;
}
case ']': {
if (tape[tapePointer] != 0) {
int nesting = 0;
while (true) {
--i;
if (code.charAt(i) == ']') {
++nesting;
continue;
}
else if (nesting > 0 && code.charAt(i) == '[') {
--nesting;
continue;
}
else if (code.charAt(i) == '[' && nesting == 0) {
break;
}
}
}
break;
}
It looks like this question has become a "post your bf interpreter" poll.
So here's mine that I just got working:
#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
void error(char *msg) {
fprintf(stderr, "Error: %s\n", msg);
}
enum { MEMSIZE = 30000 };
char *mem;
char *ptr;
char *prog;
size_t progsize;
int init(char *progname) {
int f,r;
struct stat fs;
ptr = mem = calloc(MEMSIZE, 1);
f = open(progname, O_RDONLY);
assert(f != -1);
r = fstat(f, &fs);
assert(r == 0);
prog = mmap(NULL, progsize = fs.st_size, PROT_READ, MAP_PRIVATE, f, 0);
assert(prog != NULL);
return 0;
}
int findmatch(int ip, char src){
char *p="[]";
int dir[]= { 1, -1 };
int i;
int defer;
i = strchr(p,src)-p;
ip+=dir[i];
for (defer=dir[i]; defer!=0; ip+=dir[i]) {
if (ip<0||ip>=progsize) error("mismatch");
char *q = strchr(p,prog[ip]);
if (q) {
int j = q-p;
defer+=dir[j];
}
}
return ip;
}
int run() {
int ip;
for(ip = 0; ip>=0 && ip<progsize; ip++)
switch(prog[ip]){
case '>': ++ptr; break;
case '<': --ptr; break;
case '+': ++*ptr; break;
case '-': --*ptr; break;
case '.': putchar(*ptr); break;
case ',': *ptr=getchar(); break;
case '[': /*while(*ptr){*/
if (!*ptr) ip=findmatch(ip,'[');
break;
case ']': /*}*/
if (*ptr) ip=findmatch(ip,']');
break;
}
return 0;
}
int cleanup() {
free(mem);
ptr = NULL;
return 0;
}
int main(int argc, char *argv[]) {
init(argc > 1? argv[1]: NULL);
run();
cleanup();
return 0;
}