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print line help for debug Posted on January 18th

The simplest debug technique is to print out a line contains the required variables value. By printing out a line at a suspect bugs point, it helps for debug . With few magic variables, that ease us debug even more.

They are __FUNCTION__, __PRETTY_FUNCTION__, __LINE__, __FILE__ .

__FUNCTION__ will returns a string of the function name where the print line stay.

__PRETTY_FUNCTION__ will only recognized by gcc compiler, that returns function name with indication the function is from which class.

__FILE__ returns which source code filename.

__LINE__ returns the exact line of the print line.

How to use them? Easy, you just need a printf.

printf("[DEBUG] In %s(), triggers error ...\n",__FUNCTION__);

The same way to print the filename and the line like this:

printf("Errors appear after %s %s\n",__FILE__,__LINE__);

The newer compiler will also recognized __func__ which it is part of C99 standard, it works the same as __FUNCTION__.

Reference: http://gcc.gnu.org/onlinedocs/gcc/Function-Names.html

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One Response to “print line help for debug” :

  1. This is extremely useful ;) Save a lot work to locate the buggy position.

    Commented vtian on January 21st, 2007.
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