Legal Ways to Call Void Functions in C: Statements, Comma Expressions, and Conditional Calls

A void function call is an expression of type void. You cannot assign it. You cannot pass it as an argument. You cannot use it in an arithmetic expression. But you can use it in contexts that accept void expressions: as a standalone statement, in a comma expression, and as the operand of certain operators. Understanding these contexts prevents compilation errors and clarifies what the language permits.

The ternary operator accepts void expressions in both branches. The comma operator evaluates the void call and discards it, returning the right operand. The for loop body and the if body accept void expressions as statements. What you cannot do: int z = log_msg("bad"); or printf("%d", log_msg("bad")). These require a value, and void provides none.

Void function calls are statements, not values. They fit in statement contexts: standalone, in loops, in conditionals, in comma expressions. They do not fit in value contexts: assignment, function arguments, arithmetic. The compiler enforces this. Next: segmentation faults, the crash that every C programmer meets and few fully understand.