Which C/C Identifier Should I Use to Get a Function's Name at Runtime?

Selecting the Right Identifier for Function Name Acquisition

C and C offer several identifiers for retrieving the name of the active function during runtime: __PRETTY_FUNCTION__, __FUNCTION__, and __func__. This guide explores the differences between these identifiers and provides guidance on their usage.

__func__:

"__func__" is a C99-introduced identifier that represents a character array containing the function's name. It is implicitly defined within each function. In C , func was introduced in C 11, offering an implementation-defined string.

__FUNCTION__:

"__FUNCTION__" is a pre-standard extension supported by compilers like gcc and Visual C . However, it is recommended to use func where supported and FUNCTION only when func is unavailable.

__PRETTY_FUNCTION__:

"__PRETTY_FUNCTION__" is a gcc-specific extension that resembles __FUNCTION__. For C functions, it displays the "pretty" name, including the signature. Visual C has a similar extension, __FUNCSIG__.

Deciding Which Identifier to Use:

The choice depends on compiler support and the desired function name format:

• Use func when available (supported in most modern compilers)
• Use FUNCTION if func is unavailable
• Use PRETTY_FUNCTION or FUNCSIG for the "pretty" name with the function signature (gcc or Visual C only)

Documentation:

• __func__: C99 §6.4.2.2/1
• func (C ): C 11 §8.4.1[dcl.fct.def.general]/8
• __FUNCTION__, __PRETTY_FUNCTION__: gcc documentation, "Function Names as Strings"
• __FUNCSIG__: MSDN documentation, "Predefined Macros" (Visual C )

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