Page 84 - C-Language

}

Note that even though a function defined with an empty parameter list takes no arguments, it does
not provide a prototype for the function, so the compiler will not complain if the function is
subsequently called with arguments. For example:

#include <stdio.h>

static void parameterless()
{
printf("%s called\n", __func__);
}

int main(void)
{
parameterless(3, "arguments", "provided");
return 0;
}

If that code is saved in the file proto79.c, it can be compiled on Unix with GCC (version 7.1.0 on
macOS Sierra 10.12.5 used for demonstration) like this:

$ gcc -O3 -g -std=c11 -Wall -Wextra -Werror -Wmissing-prototypes -pedantic proto79.c -o
proto79
$

If you compile with more stringent options, you get errors:

$ gcc -O3 -g -std=c11 -Wall -Wextra -Werror -Wmissing-prototypes -Wstrict-prototypes -Wold-
style-definition -pedantic proto79.c -o proto79
proto79.c:3:13: error: function declaration isn’t a prototype [-Werror=strict-prototypes]
static void parameterless()
^~~~~~~~~~~~~
proto79.c: In function ‘parameterless’:
proto79.c:3:13: error: old-style function definition [-Werror=old-style-definition]
cc1: all warnings being treated as errors
$

If you give the function the formal prototype static void parameterless(void), then the compilation
gives errors:

$ gcc -O3 -g -std=c11 -Wall -Wextra -Werror -Wmissing-prototypes -Wstrict-prototypes -Wold-
style-definition -pedantic proto79.c -o proto79
proto79.c: In function ‘main’:
proto79.c:10:5: error: too many arguments to function ‘parameterless’
parameterless(3, "arguments", "provided");
^~~~~~~~~~~~~
proto79.c:3:13: note: declared here
static void parameterless(void)
^~~~~~~~~~~~~
$

Moral — always make sure you have prototypes, and make sure your compiler tells you when you
are not obeying the rules.

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