My program is supposed to fork three processes. Each of these processes will create three threads and fork two additional processes. These two additional processes will create three threads.
Here is my code. I've tried to keep things simple with nested loops. I think at some point I might be forking more processes or creating more threads.
#include <pthread.h>
#include <stdio.h>
#include <stdlib.h>
void *printme(void* Array){
int *Arr = (int *) Array;
int len = sizeof(Arr) / sizeof(int);
if (len == 1){
printf("I'm thread %d.%d",Arr[0],Arr[1]);
}
else if (len == 2){
printf("I'm thread %d.%d.%d",Arr[0],Arr[1],Arr[2]);
}
printf("\n");
pthread_exit(NULL);
}
int main(void){
int i, j, k, l;
int threadLevel1[2];
int threadLevel2[3];
printf("\n");
for (i = 1 ; i < 4 ; i++){ // Loop to fork the three main processes.
if (fork() != 0){
sleep(4);
}
else{
//The newly forked process will create three threads and fork two additional processes.
for (j = 1 ; j < 4 ; j++){
pthread_t t;
threadLevel1[0] = i;
threadLevel1[1] = j;
if (pthread_create(&t, NULL, printme, (void*) threadLevel1) != 0){
perror("pthread_create");
exit(1);
}
}
for (k = 1; k < 3 ; k++){
pid_t a = fork();
if (a != 0){
sleep(2);
}
else if (a == -1){
perror("fork"); /* display error message */
exit(0);
}
else{
for (l = 1 ; l < 4 ; l++){
pthread_t t;
threadLevel2[0] = i;
threadLevel2[1] = k;
threadLevel2[2] = l;
if (pthread_create(&t, NULL, printme, (void*) threadLevel2)!=0) {
perror("pthread_create");
exit(1);
}
}
}
}
}
}
return 0;
}
You have a problem in your code here:
void *printme(void* Array){
int *Arr = (int *) Array;
int len = sizeof(Arr) / sizeof(int);
The value len will always be the same no matter what is passed in to printme. That's because C passes arrays as pointers, not as objects with embedded lengths.
Related
I'm trying to create a char matrix using dynamic allocation (char**). It represents a board where the margins are '#' character and in the middle is the ASCII 32 (blank space). When I run the code this massage appear: "Exception thrown at 0x00007FFD9ABF024E (ucrtbased.dll) in myapp.exe: 0xC0000005: Access violation reading location " in some cpp file.
Here's my code:
#include <iostream>
using namespace std;
char** allocateBoard(int n)
{
char** Board = 0;
Board = new char* [n+2];
int i;
for (i = 0; i < n + 2; i++)
{
Board[i] = new char[n * 2 + 2];
}
return Board;
}
void initBoard(char**& Board, int n)
{
int i, j;
for (i = 0; i < n; i++)
{
for (j = 0; j < n * 2; j++)
{
if (i == 0 || i == n - 1) Board[i][j] = '#';
else if (j == 0 || j == n * 2 - 1) Board[i][j] = '#';
else Board[i][j] = 32;
}
}
}
void showBoard(char** Board, int n)
{
int i, j;
for (i = 0; i < n; i++)
{
for (j = 0; j < n * 2; j++)
{
cout << Board[i][j];
}
cout << endl;
}
}
int main()
{
int n = 4;
char** Board = 0;
Board = allocateBoard(n);
initBoard(Board, n);
showBoard(Board, n);
cout << endl;
showBoard(Board, n);
for (int i = 0; i < n * 2 + 4; i++)
{
delete[] Board[i];
}
delete[] Board;
return 0;
}
Does anyone know where is the problem? As a very beginner I can't see where is the mistake. I've allocated more space in the matrix than I'm actually using so I can't figure why this message appears. Is the deallocation the problem?
Thanks!
I need to make a c program that will make a histogram of all the letters present in a phrase the user gives. When I run it, I does it but gives a "* stack smashing detected *: terminated". Where would this error be coming from? (for ease right now I set max to 3). In the future i'll have it find the max
Thank you
Andrew
#include <stdio.h>
#include <ctype.h>
#include <string.h>
static void ReadText(int histo[26],int max) {
char phrase[100];
int i;
char Letter;
char toArray;
// read in phrase
printf("Enter Phrase: "); // reads in phrase with spaces between words
scanf("%[^\n]",phrase);
// count the number of certain letters that occur
for(i = 0; i <= strlen(phrase);++i) {
Letter = phrase[i];
if(isalpha(Letter) != 0){
Letter = tolower(Letter);
toArray = Letter - 97;
histo[(int)toArray] = histo[(int)toArray] + 1;
}
}
}
static void DrawHist(int histo[26], int max){
int i;
int j;
int histo2[50];
for(i = 0; i <= 26; i++) {
histo2[i+i] = histo[i];
if(i < 25) {
histo2[i+i+1] = 0;
}
}
// (i = 1; i <= 50; i++) {
// printf("%d",histo2[i]);
//}
//printf("\n");
for(i=max;i>0;--i) {
for(j=0;j<=51;++j) {
if((j < 51) && (histo2[j] >= i)) {
printf("|");
}
else if((j < 51) && (histo2[j] < i)){
printf(" ");
}
else if(j == 51){
printf("\n");
}
}
}
printf("+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-\n");
printf("A B C D E F G H I J K L M N O P Q R S T U V W X Y Z\n");
}
int main() {
int histo[26] = {0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0};
int max = 3;
//int i;
ReadText(histo,max);
//for(i = 0; i<26;++i) {
// printf("%d",histo[i]);
//}
DrawHist(histo,max);
return 0;
}
Could anyone please help me understand why Clang reallocates the same memory address for different variables while their lifetimes intersect?
I am using a sample program (below) to show the problem.
When I compile the program with clang -O0, variable j in function ok has the same memory address as variable solutions in function nqueens.
Function ok is called inside function nqueens, which means that the lifetime of the variables intersect; the same stack space cannot be used/reused for both functions.
Compiling the program with gcc or clang at -O1, however, they are assigned different memory addresses.
Any help is appreciated!
#include <stdlib.h>
#include <stdio.h>
#include <memory.h>
#include <alloca.h>
/* Checking information */
static int solutions[] = {
1,
0,
0,
2,
10, /* 5 */
4,
40,
92,
352,
724, /* 10 */
2680,
14200,
73712,
365596,
};
#define MAX_SOLUTIONS sizeof(solutions)/sizeof(int)
int total_count;
int sharedVar = 0;
int ok(int n, char *a)
{
int i, j;
char p, q;
printf("jjjjjjjjj: %d, %p\n", n,&j);
for (i = 0; i < n; i++) {
p = a[i];
for (j = i + 1; j < n; j++) {
q = a[j];
if (q == p || q == p - (j - i) || q == p + (j - i))
return 0;
}
}
return 1;
}
void nqueens (int n, int j, char *a, int *solutions)
{
int i,res;
sharedVar = sharedVar * j - n;
if (n == j) {
/* good solution, count it */
*solutions = 1;
return;
}
printf("solutions: %d, %p\n", j, &solutions);
*solutions = 0;
/* try each possible position for queen <j> */
for (i = 0; i < n; i++) {
a[j] = (char) i;
if (ok(j + 1, a)) {
nqueens(n, j + 1, a,&res);
*solutions += res;
}
}
}
int main()
{
int size = 3;
char *a;
// printf("total_count: %p\n", &total_count);
total_count=0;
a = (char *)alloca(size * sizeof(char));
printf("Computing N-Queens algorithm (n=%d) ", size);
sharedVar = -5;
nqueens(size, 0, a, &total_count);
printf("completed!\n");
printf("sharedVar: %d\n", sharedVar);
}
I wrote a rot13.c program but I can tell something in my loop inside rot13_translate_string is causing the program to just print out blank lines.
Any thoughts?
Thank you!
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
char rot13_translate_character(char c)
{
if( 'A' <= c && c <= 'M' )
{
return c + 13;
}
else if( 'N' <= c && c <= 'Z' )
{
return c - 13;
}
else if( 'a' <= c && c <= 'm' )
{
return c + 13;
}
else if( 'n' <= c && c <= 'z' )
{
return c - 13;
}
else
{
return c;
}
}
char *rot13_translate_string(const char *str)
{
int len = strlen(str);
char *translation = calloc(len, sizeof(char));
int i;
do //****HERE IN THIS SECTION
{
/* Translate each character, starting from the end of the string. */
translation[len] = rot13_translate_character(str[len]);
len--;
} while( len < 0 ); //<
return translation;
}
And here is the main (part of the same file) - is the condition for my for i = 1 ok?
int main(int argc, char **argv)
{
if( argc < 2)
{
fprintf(stderr, "Usage: %s word [word ...]\n", argv[0]);
return 1;
}
/* Translate each of the arguments */
int i;
for( i = 1; i < argc; i++) //*****IS this right?
{
char *translation = rot13_translate_string( argv[i] );
fprintf(stdout, "%s\n", translation);
}
return 0;
}
As just it was pointed out by Janis is the control on the loop do ... while. It should be
while( len >= 0 );
A "while" loop runs while the control expression is true (and terminates once the expression becomes false). You define the variable len just before the loop and it cannot be <0.
So you never really enter in the loop.
You obtain a line for each input word because of fprintf(stdout, "%s\n", translation); line, where you print for each (empty) word a line (\n).
In other languages, for example in Pascal, there is "repeat until" loop construction, which continues to run until the control expression is true, and only after that it changes it terminates.
In that case you could use a condition with <0.
In C to follow the same logic you can use while loop and negate the condition. In your case
} while (! (len < 0) );
I get _CrtIsValidHeapPointer(pUserData) error when running the code above.
Sometimes the code works perfectly, and sometimes this message appears. So I guess the problem is related to the memory allocation. But I've gone through the code many times and the numbers make sence to me (and also when debugging).
I noticed it happens in line "free(str_temp)" at the debugging.
The relevant code is here:
int main(){
int n;
int len;
char *str;
char command[3];
printf("Enter your string:\n");
scanf("%d", &n);
str = malloc(n+1);
scanf("%s", str);
while (1){
printf(">");
scanf("%s", command);
if (compare(command, "ml")) {
int k;
scanf("%d", &k);
multiply(str, n, k);
printf("Current string is %s\n", str);
n = ln(str);
continue;
}
free(str);
return 0;
}
void multiply(char *str, int n, int k) {
char *str_temp = malloc(n+1);
int i;
int j;
int q;
for (i = 0; i < n; i++){
str_temp[i] = str[i];
}
str_temp[n] = '\0';
free(str);
*str = malloc(n*k+1);
for (i = 0; i < k; i++){
for (j = 0; j < n; j++){
str[i*n + j] = str_temp[j];
}
}
str[n*k] = '\0';
free(str_temp);
}
Try to use message defination
void multiply(char **str, int n, int k)//Use **str(double pointer) instead of *str.
And call it like
multiply(&str, n, k);