Is it legal to return an expression of type void?
c, c++, clang, gcc, language-lawyer
Solution
C11, 6.8.6.4 "The `return` statement":
A `return` statement with an expression shall not appear in a function whose return type is `void`.
No, you may not use an expression, even if it is of `void` type.
From the foreword of the same document:
Major changes in the second edition included:
[...]
- `return` without expression not permitted in function that returns a value (and vice versa)
So this was a change from C89 -> C99 (the second edition of the language standard), and has been that way ever since.
C++14, 6.6.3 "The `return` statement":
A return statement with an expression of non-void type can be used only in functions returning a value [...] A return statement with an expression of type void can be used only in functions with a return type of cv void; the expression is evaluated just before the function returns to its caller.
Yes, you may use an expression if it is of void type (that's been valid since C++98).
Problem
This compiles without any warnings. Is this legal in C and C++ or does it just work in gcc and clang? If it is legal, is it some new thing after C99? ``` void f(){} void f2(){ return f(); } ``` Update as "Rad Lexus" suggested I tried this: ``` $ gcc -Wall -Wpedantic -c x.c x.c: In function ‘f2’: x.c:7:9: warning: ISO C forbids ‘return’ with expression, in function returning void [-Wpedantic] return f(); ``` ``` $ clang -Wall -Wpedantic -c x.c x.c:7:2: warning: void function 'f2' should not return void expression [-Wpedantic] return f(); ^ ~~~~~ 1 warning generated. ``` ``` $ gcc -Wall -Wpedantic -c x.cc (no errors) ``` ``` $ clang -Wall -Wpedantic -c x.cc (no errors) ``` Update Someone asked how this construction is helping. Well is more or less syntactic sugar. Here is one good example: ``` void error_report(const char *s){ printf("Error %s\n", s); exit(0); } void process(){ if (step1() == 0) return error_report("Step 1"); switch(step2()){ case 0: return error_report("Step 2 - No Memory"); case 1: return error_report("Step 2 - Internal Error"); } printf("Processing Done!\n"); } ```