Function Logger

Table of Contents

• About
• Building from source
• Linking
• Common issues
• Usage

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About

A cross-platform library, written in C, to log information from the runtime of a program and output it to a file and/or the console.

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Building from source

To build the library from source, simply open your terminal/command prompt and type one of the following:

# Build both the static and shared library
make

# Build just the static library
make staticlib

# Build just the shared library
make sharedlib

You can also build the provided test program by typing the following:

# Build the test program linking against the shared library
make test-shared

# Build the test program linking against the static library
make test-static

The libraries also have debug variants that can be built by appending DEBUG=yes to your make command

# Builds both the static and shared debug versions of the library
make DEBUG=yes 

# Builds the test program, linking against the static library, in
# debug mode, using the debug library
make test-static DEBUG=yes

Note

For Windows users, this library has been built and tested using the MSYS2 suite of build tools, not Visual Studio. If you intend on using or building the library with Visual Studio, your mileage may vary as to whether it will actually work or not.

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Linking

In order to properly link, you have to add -lfunclog to your linked libraries as well as the path it is located in. Here is the example from the provided test program:

# Linking against the static library
LIBS = -L 'libs/release/static -lfunclog'

# Linking against the shared library
LIBS = -L 'libs/release/shared -lfunclog'

Linking against the shared library

When linking with the shared library on macOS and GNU/Linux, you need to add an rpath to point to the location of the shared library by adding an LDFLAG. Again, here is the example from the provided test program:

LDFLAGS = -Wl,-rpath 'libs/release/shared'

Doing this will ensure your program can actually find the library when you try to run it.

On Windows, make sure the dll is in the same directory as your executable.

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Common issues

Linking with the static library is fairly straight forward. However, linking with the shared library can pose issues.

-lfunclog not found

If you run into an error message saying:

ld: library not found for -lfunclog
# OR
/usr/bin/ld: cannot find -lfunclog: No such file or directory

The reason this is happening is due to the linker being unable to find the libfunclog.so or libfunclog.dylib file respectively. Most likely, the cause is that you only have the libfunclog.so.x.x.x or libfunclog.x.x.x.dylb in the folder you specified with your -L flag. To fix this, create a symbolic link as seen below:

# GNU/Linux
ln -s libfunclog.so.x.x.x libfunclog.so

# macOS
ln -s libfunclog.x.x.x.dylb libfunclog.dylb

Alternatively, rather than passing -L /path/to/lib -lfunclog, you could just give the path to the shared library, as seen below:

# Errors saying it can't find -lfunclog
gcc example.c -o example -lfunclog -L libs -Wl,-rpath 'libs'

# No errors
gcc example.c -o example libs/libfunclog.so.1.0.0 -Wl,-rpath 'libs'

Code compiles, but unable to find the shared library

Similar to the error above, if your code compiles but you get a message saying something to the effect of it can't find libfunclog.so.x.x.x or libfunclog.x.x.x.dylb, this is due to you not having said file in your rpath. To fix this, make sure the directory you are specifying as your rpath contains libfunclog.so.x.x.x or libfunclog.x.x.x.dylb depending on your platform.

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Usage

Usage of the library has three components, linking (which we discussed above), including, and calling the functions.

Including

First, ensure you are including the header file log.h in your program.

#include "log.h"

You also need to ensure the directory where you put the log.h file is included in your project. For example, if you have a headers/ folder where you added log.h, you would need -I headers/ in your makefile.

Using in your program

The library includes four functions to allow you to log your information. All of which function just like printf() in terms of syntax. The only difference is in the LOGF()/NLOGF() and LOGFL()/NLOGFL() functions, which require you to add the level of logging you would like.

// Don't auto print a new line at the end
#define LOG(...)
#define LOGL(level, ...)
#define LOGF(...)
#define LOGFL(level, ...)

// Do auto print a new line at the end
#define NLOG(...)
#define NLOGL(level, ...)
#define NLOGF(...)
#define NLOGFL(level, ...)

While not required, it is best practice to initialize the logger at the beginning of your program with init_logger and call log_cleanup at the end to ensure all allocated memory is released. If you wish to log output to a file, calling init_logger is required.

Example code

#include <stdio.h>
#include <string.h>
#include "log.h"

int main(int argc, char **argv)
{
    if(argc != 2)
    {
        LOGFL(ERROR, "%s takes one argument\n", argv[0]);
        LOG("Usage: %s [name]\n");
        return -1;
    }

    init_logger(INFO, "logs", argv, true, true);
    NLOG("Hello %s!", argv[1]);
    log_cleanup();
    
    return 0;
}

The above program initializes the logger, so only messages of debug level INFO or higher will be logged. The next argument tells the logger to save logs to a directory called logs/. Passing in argv adds the name of the program to the log file name, along with a timestamp as to when the file was generated. Lastly, the first true tells the logger to save the data to a file, and the second true tells the logger to also write the data to the console.

Assuming you called the program example.c and had log.h and that static version of the library in the same directory, it could be compiled with the following command:

gcc example.c -o example -L ./ -lfunclog

Example output

Below is some example output from the logger:

Log from LOG()
[INFO]    Log from LOGL() at level 3
[07/10/23@21:25:05][main():test.c:38] Log from LOGF()
[07/10/23@21:25:05][main():test.c:39] [DEBUG]   Log from LOGFL() at level 2
[07/10/23@21:25:05][main():test.c:40] [WARNING] Log from LOGFL() at level 4