C - gcc: no compiler warning with different function-declaration/implementation

Question

I try to figure out why my c-compiler gives me no warning/error with following (simplified) code.

The function-declaration have no parameters while the function-implemen

Answer 1

In C this function declaration

void foo();

means that there is nothing known about the function parameters in the point of the declaration.

The types and number of the parameters are deduced from a function call.

As for your program then this call

foo();

has undefined behavior because the number of parameters and the number of arguments mismatch.