Predefined variable of the name of the function being compiled.
static const char __func__[] = "function-name";
The compiler implicitly defines this variable at the beginning of each function if the function refers to __func__. The character string contained by this array, function-name, is the name of the function being compiled.
This implicit variable is undefined outside of a function body. This variable is also undefined when C99 (ISO/IEC 9899-1999) or GCC (GNU Compiler Collection) extension settings are off.