CODEWITHSUNDEEP
iphoneobjective-ccios
Anthony Blake
Anthony Blake

Reputation: 5348

NSLog style debug messages from C code

I have some C code in a static library that I'm compiling into an iPhone app. I'd like to print some debug messages to the console; is there something like NSLog I should use? I'm guessing NSLog only works for the Objective-C parts of the program.

EDIT: fprintf(stdout, fmt...) and fprintf(stderr, fmt...) don't work either.. any idea why they don't? Should they work?

Upvotes: 15

Views: 9950

Answers (8)

Isma Rekathakusuma
Isma Rekathakusuma

Reputation: 1152

While printf will show up if you're debugging from XCode, it won't show up in the Organizer Console. You can run the following command to print only to device's console:

syslog(LOG_WARNING, "log string");

You will also need to #include <sys/syslog.h> for syslog and LOG_WARNING to be explicitly declared

Upvotes: 0

coldfire
coldfire

Reputation: 1005

Other solution:

#include <CoreFoundation/CoreFoundation.h>
extern "C" void NSLog(CFStringRef format, ...);

#define MyLog(fmt, ...) \
{ \
    NSLog(CFSTR(fmt), ##__VA_ARGS__); \
}

MyLog("val = %d, str = %s", 123, "abc");

Upvotes: 4

Tomer
Tomer

Reputation: 3297

#include <asl.h>
...
asl_log(NULL, NULL, ASL_LEVEL_ERR, "Hi There!");

Note that lower priority levels such as ASL_LEVEL_INFO may not show up in console.

Upvotes: 2

Walt Sellers
Walt Sellers

Reputation: 3939

You probably need to use the Apple System Log facility to get the output into the device console.

Check the functions in usr/asl.h. 

asl_open
asl_new
asl_set
asl_log
asl_free

Upvotes: 0

Tomer
Tomer

Reputation: 3297

You can make a wrapper for NSLog if you mix Objective-C code like this:

log.h

void debug(const char *message, ...) __attribute__((format(printf, 1, 2)));

log.m

#import <Foundation/Foundation.h>
#import "log.h"

void debug(const char *message,...)
{
    va_list args;
    va_start(args, message);
    NSLog(@"%@",[[NSString alloc] initWithFormat:[NSString stringWithUTF8String:message] arguments:args]);
    va_end(args);
}

and then, in your C file:

#include "log.h"
...
debug("hello world! variable: %d", num);

Upvotes: 10

paleozogt
paleozogt

Reputation: 6563

While printf will show up if you're debugging from XCode, it won't show up in the Organizer Console. You can use what NSLog uses: CFLog or syslog.

Upvotes: 3

El Developer
El Developer

Reputation: 3346

You should be able to see printf or fprintf statements. Try running some of the code in the library but from the terminal, something should appear if not. A much more complicated (and even silly/stupid/wrong) method that I will guarantee you that will work would be:

sprintf(message,"This is a log line %s",someString);
system("echo %s",message);

If that doesn't work then you probably have something weird in your code.

Note: This will probably only work in the simulator.

Upvotes: 0

Michael Dautermann
Michael Dautermann

Reputation: 89509

you can always do the classic:

fprintf(stderr, "hi, this is a log line: %s", aStringVariable);

Upvotes: 11

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