Page 192 - C-Language

}

int test_function(int fruit)
{
fruit += 1;
return fruit;
}

Note that you get puzzling error messages if you introduce a type name in a prototype:

int function(struct whatever *arg);

struct whatever
{
int a;
// ...
};

int function(struct whatever *arg)
{
return arg->a;
}

With GCC 6.3.0, this code (source file dc11.c) produces:

$ gcc -O3 -g -std=c11 -Wall -Wextra -Werror -c dc11.c
dc11.c:1:25: error: ‘struct whatever’ declared inside parameter list will not be visible
outside of this definition or declaration [-Werror]
int function(struct whatever *arg);
^~~~~~~~
dc11.c:9:9: error: conflicting types for ‘function’
int function(struct whatever *arg)
^~~~~~~~
dc11.c:1:9: note: previous declaration of ‘function’ was here
int function(struct whatever *arg);
^~~~~~~~
cc1: all warnings being treated as errors
$

Place the structure definition before the function declaration, or add struct whatever; as a line
before the function declaration, and there is no problem. You should not introduce new type
names in a function prototype because there's no way to use that type, and hence no way to
define or use that function.

File Scope

#include <stdio.h>

/* The identifier, foo, is declared outside all blocks.
It can be used anywhere after the declaration until the end of
the translation unit. */
static int foo;

void test_function(void)
{

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