Ideally I'd like to setup a selector to see every time NSLog is called in my app, and to get the output of that NSLog. NSLog might be called by an SDK I'm using and I'd like to be able to see the output of those logs from within my app. Is that possible?
What you want is a Symbolic breakpoint.
Navigate to the Breakpoints tab in Xcode and use the + button in the bottom left corner to add one.
When the breakpoint is added, it should automatically come up with a window that allows you to enter the conditions on which you want it to pause execution. You can use NSLog as the symbol.
As for calling a custom function of your own, you can attempt to do that by adding an action in that breakpoint and utilise the debugger's ability to call into your own code by passing in the arguments that are available to the debugger e.g. $arg1.
So I dont think it is possible to simply replace every instance of NSLog with something else... but you could do something like this:
#define NSLog MyLog
void MyLog(NSString *format, ...) NS_FORMAT_FUNCTION(1,2);
void MyLog(NSString *format, ...)
{
va_list list;
va_start(list,format);
NSLogv(format,list);
va_end(list);
va_start(list,format);
vfprintf(stderr,[format UTF8String], list);
va_end(list);
}
int main(int argc, const char * argv[]) {
NSLog(#"hello %s\n","world");
return 0;
}
My example uses 2 va_lists to log with an NSLog like NSLogv and vfprintf to log to an open FILE * stream (stderr in this case)... you could also probably more simply format an NSString (as vfprintf can't print NS objects)...
I tried a little bit to try to re-assign NSLog with dlsym which would be process wide, rather than just when the macro is expanded... I couldn't get it to work but I am not a dynamic linker expert.
Related
I just started doing some competitive programmning in objective C. There's a problem which I'm facing, most sites start with main.m
int main(int argc, char * argv[]) {
#autoreleasepool {
}
}
I somehow learned how to get input and use it. But today I tried a differnt work where
void main()
{
}
when I tried scanf("%s",str) though I could read the first line of input. But I don't know how to start and how to get rest of lines.
I want to lean more about console input/output in iOS. Any help will be much appreciated?
What you need is a bit of a tutorial
If you right click any data structure for instance there'l be a first option "print description" another option with your code : NSLog(name of variable); for e.g for an array : NSLog(#"%#",myArray);
Lastly,Typing po myarray in the right half of the console (under lldb) would print out myArray's contents
Hope this helps! Cheers
When I clean, build and run my XCode project all goes well, but if I open a file that calls the function, an Use of undeclared identifier 'func()' appears. This is the whole implementation:
The function is called:
func();
And 'func()' is decleared in a .h file like so:
#if __cplusplus
extern "C" {
#endif
extern void func();
#if __cplusplus
}
#endif
and func() is implemented is a cplusplus library.
Why would the error ONLY appears if the file is open, but if I don't open it, it runs and works just fine?
Xcode has two ways of generating error messages. Usually both of these generate the same messages, so you do not detect that there are two systems.
The first system is the editor which does syntax coloring and auto-completion. It will also show error messages almost instantly after you write an error.
The second system is errors shown in the build log.
I suspect that your project has a complicated include setting. This prevents the first system from finding the correct file to include and therefore it cannot find the definition of func().
I believe ive looked at every article related to keyboard input, but still cant get it to work. ALl i want is a output, using NSLog everytime i hit a key, in the app or not. Im currently using xcode 5. Ive tried many snippets of code such as
[NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask handler:^(NSEvent *event)
NSLog(#"%#",event.characters);
and im not sure where to put his code. Do i put it in the main function like this
#import <Foundation/Foundation.h>
#import <appkit/NSEvent.h>
int main(int argc, char * argV[]) {
#autoreleasepool{
[NSEvent addGlobalMonitorForEventsMatchingMask:NSKeyDownMask handler:^(NSEvent *event)
NSLog(#"%#",event.characters);
}
}
Clearly im new to objective-C, and i dont plan on continuing with it unless i can get keyboard input to work. Ive tried tutorials, snippets from keyloggers, and the mac dev forums. Thanks.
Your code is pretty close but you're getting hung up on block syntax. Blocks are very powerful and useful, but the syntax is truly awful and I still struggle with it 2 years after starting to work with them. Blocks are much less readable than C function pointers, and that's saying a lot.
It should look like this:
int main(int argc, char * argV[])
{
#autoreleasepool
{
[NSEvent addGlobalMonitorForEventsMatchingMask: NSKeyDownMask
handler: ^(NSEvent *event)
{
NSLog(#"%#",event.characters);
}
];
}
}
I put all the opening and closing braces on separate lines for clarity. A block needs to be enclosed in braces, and you were missing braces, as well as the closing bracket on your call to addGlobalMonitorForEventsMatchingMask:handler:
BTW, it's very unusual to change the main() function on a Mac or iOS program. Usually you leave that alone, and then set up an application object, set up a delegate, and put your custom code in the app delegate.
You should start of using the normal Cocoa design patterns for applications, and not try to toss them.
If you want to work with main() in C style you should think about creating a command line tool intend of an interactive application. You're going to set yourself up for failure if you don't follow the standard patterns. There's just too many ways to get things wrong.
Your main is missing the housekeeping needed to create a working iOS or Mac application
Hi this is third day of mine using Objective-C today I was writing few simple programs and i ecncountered the following warning
main.m:19:5: warning: passing argument 1 of 'NSLog' makes pointer from integer without a cast [enabled by default]
NSLog(res);
which finally resulted in the Segmentation fault.. Here is my program..
#import <Foundation/Foundation.h>
#interface SomeClass: NSObject
{
int x;
}
#property int x;
#end
#implementation SomeClass
#synthesize x;
#end
int main(){
NSAutoreleasePool * pool = [[NSAutoreleasePool alloc]init];
SomeClass * obj = [[SomeClass alloc]init];
obj.x =20;
int res = obj.x;
NSLog(res); //error
/* But the error was not seen when I replaced the above statement with
NSLog(#"The value is : %d",res);
*/
[pool drain];
return 0;
}
The error message that I got was :
Compiling the source code....
$gcc `gnustep-config --objc-flags` -L/usr/GNUstep/System/Library/Libraries -lgnustep-base main.m -o demo -lm -pthread -lgmpxx -lreadline 2>&1
main.m: In function 'main':
main.m:19:5: warning: passing argument 1 of 'NSLog' makes pointer from integer without a cast [enabled by default]
NSLog(res);
^
In file included from /usr/GNUstep/System/Library/Headers/Foundation/NSObject.h:30:0,
from /usr/GNUstep/System/Library/Headers/Foundation/FoundationErrors.h:29,
from /usr/GNUstep/System/Library/Headers/Foundation/Foundation.h:33,
from main.m:1:
/usr/GNUstep/System/Library/Headers/Foundation/NSObjCRuntime.h:146:16: note: expected 'struct NSString *' but argument is of type 'int'
GS_EXPORT void NSLog(NSString *format, ...) NS_FORMAT_FUNCTION(1,2);
^
Executing the program....
$demo
Segmentation fault (core dumped)
Please help by making me understand why NSLog behaves like this ? Where did I go wrong?
Thank you...
You can't use the NSLog like this, You need to specify the control string and use like:
NSLog(#"%d",res);
The format should be specified for NSLog(), please check the NSLog and NSLogv reference for more information
NSLog
Logs an error message to the Apple System Log facility.
void NSLog ( NSString *format, ... );
Discussion
Simply calls NSLogv, passing it a variable number of arguments.
Availability
NSLogv
Logs an error message to the Apple System Log facility.
void NSLogv ( NSString *format, va_list args );
Discussion
Logs an error message to the Apple System Log facility (see man 3
asl). If the STDERR_FILENO file descriptor has been redirected away
from the default or is going to a tty, it will also be written there.
If you want to direct output elsewhere, you need to use a custom
logging facility.
The message consists of a timestamp and the process ID prefixed to the
string you pass in. You compose this string with a format string,
format, and one or more arguments to be inserted into the string. The
format specification allowed by these functions is that which is
understood by NSString’s formatting capabilities (which is not
necessarily the set of format escapes and flags understood by printf).
The supported format specifiers are described in “String Format
Specifiers”. A final hard return is added to the error message if one
is not present in the format.
In general, you should use the NSLog function instead of calling this
function directly. If you do use this function directly, you must have
prepared the variable argument list in the args argument by calling
the standard C macro va_start. Upon completion, you must similarly
call the standard C macro va_end for this list.
Output from NSLogv is serialized, in that only one thread in a process
can be doing the writing/logging described above at a time. All
attempts at writing/logging a message complete before the next thread
can begin its attempts.
The effects of NSLogv are not serialized with subsystems other than
those discussed above (such as the standard I/O package) and do not
produce side effects on those subsystems (such as causing buffered
output to be flushed, which may be undesirable). Availability
You cant declare the NSLog like that see the tutorial for NSLog its may be useful for you.
Objective-C has a number of built-in data types:
int – integer constant
float – real numbers with fractional component
double – double precision floating point number
char – a single character
short – short integer (2 bytes)
long – double short
long long – double long
BOOL – boolean
The utility function NSLog() can be used to print to the debug console in Xcode. NSLog() uses the NSString formatting services. The easiest way to create a NSString is to use the #”" notation. Inside a format string a % is a placeholder for a value. The character after the % determines the value expected, be it an int or a float and so on. If we declare an integer “int i = 5″ and want to print the value of i with NSLog() we can do it with NSLog(#”The value of i is %d”, i);
You can use %d to print the value of an int, %f for a float and double, %c for a char. For a full listing of all format specifiers supported by NSString formatting methods read through the documentation.
For More Reference Click Here
keep learning..:)
The 1st argument to NSLog is an NSString that should be a string with 0 or more format specifiers.
Use:
NSLog(#"res = %d", res);
or just:
NSLog(#"%d", res);
Have a look at the reference docs for NSLog for details.
You should specify the compiler that what kind of data type you want to print in Log,
NSLog(#"%d",res);
You should not never use NSLog(variable) directly. Instead, use NSLog(#"%d", variable) for integers or NSLog(#"%#", object) for objects.
I'm developing one logger class for my application.NSLog will be printed only in debug mode. I have customized the NSLog where Name of the source file,Source code line number,Name of the class and method where NSLog() was called is printed.
That is , my current NSLOG looks like
(ClassName MethodName) (SourceFileName:LineNumber) NSLog output
Now, I want to log, parameter values of the methodname. How to get those parameter values in NSLog???
I want the output as
(ClassName MethodName) (SourceFileName:LineNumber) (Parameter Values) NSLog output
Something like this should work
#define InstanceLog(fmt, ...) NSLog(#"(%#.%#)(%s:%d) " fmt, NSStringFromClass(self.class), NSStringFromSelector(_cmd), __FILE__, __LINE__, ##__VA_ARGS__)
You may use it as NSLog within Objective-C methods
InstanceLog(#"simple string");
InstanceLog(#"%# %#", #"hello", #"world");
There isn't a way to automatically introspect the values passed to a method. Even in DEBUG builds (where the optimizer is out of the way), any attempts to write code to introspect said iVars is going to be incredibly complex (you'll have to dive into the symbol tables, extract offsets, etc, and then try and find the arguments that were likely destroyed in the attempt to grab them).
So, no, no way to really automate that.
In general, though, any such logging mechanism would generate such an atrociously huge amount of output that you are far better off creating (potentially debugging only) logging that is both configurable and highly tuned to your application.
You can pass args like this (thanks to #hoha for the simpler version).
#import <Foundation/Foundation.h>
#define FooLog(fmt, ...) NSLog(#"(%s): %#", __PRETTY_FUNCTION__, ## __VA_ARGS__)
#interface Bob:NSObject
#end
#implementation Bob
- (void)yourUncle
{
FooLog(#"%#", self);
}
#end
int main(int argc, char *argv[]) {
#autoreleasepool {
NSString *w = #"World";
FooLog(#"Hello, %#!", w);
[[Bob new] yourUncle];
}
}
Output:
2013-09-02 10:51:49.447 Untitled[60967:507] (int main(int, char **)): Hello, World!
2013-09-02 10:51:49.453 Untitled[60967:507] (-[Bob yourUncle]): <Bob: 0x7fde8840a490>
for handle custom logging you can use or refer following link.
You can customise Lumberjack as per you needs.
Lumberjack error logging for ios
Lumberjack error logging tutorial