Before we start discussing about __func__, let us write some code snippet and anticipate the output:
Will it compile error due to not defining variable __func__ ? Well, as you would have guessed so far, it won’t give any compile error and it’d print main!
C language standard (i.e. C99 and C11) defines a predefined identifier as follows in clause 184.108.40.206:
“The identifier __func__ shall be implicitly declared by the translator as if, immediately following the opening brace of each function definition, the declaration
static const char __func__ = “function-name”;
appeared, where function-name is the name of the lexically-enclosing function.”
It means that C compiler implicitly adds __func__ in every function so that it can be used in that function to get the function name. To understand it better, let us write this code:
And it’ll give output as foobar. A use case of this predefined identifier could be logging the output of a big program where a programmer can use __func__ to get the current function instead of mentioning the complete function name explicitly. Now what happens if we define one more variable of name __func__
Since C standard says compiler implicitly defines __func__ for each function as the function-name, we should not defined __func__ at the first place. You might get error but C standard says “undefined behaviour” if someone explicitly defines __func__ .
Just to finish the discussion on Predefined Identifier __func__, let us mention Predefined Macros as well (such as __FILE__ and __LINE__ etc.) Basically, C standard clause 6.10.8 mentions several predefined macros out of which __FILE__ and __LINE__ are of relevance here.
It’s worthwhile to see the output of the following code snippet:
Instead of explaining the output, we will leave this to you to guess and understand the role of __FILE__ and __LINE__!
Please do Like/Tweet/G+1 if you find the above useful. Also, please do leave us comment for further clarification or info. We would love to help and learn 🙂
- Why to use fgets() over scanf() in C?
- Thread functions in C/C++
- How to Compile and Run C/C++/Java Programs in Linux
- How to get the current position of cursor from output screen in C?
- Methods to concatenate string in C/C++ with Examples
- Compiling with g++
- Why learning C Programming is a must?
- Lex program to count the number of lines, spaces and tabs
- C program to check if a given string is Keyword or not
- Difference between scanf() and gets() in C
- Dividing a Large file into Separate Modules in C/C++, Java and Python
- C program to store Student records as Structures and Sort them by Name
- Step by Step guide to Write your own WordPress Template
- Similarities and Differences between Ruby and C language