function declared inside other

[BEN10]

here's a code

#include <stdio.h>
void f2(void);
int main(void)
{
	void f1(void);
	f1();
                f2();
	getch();
	return 0;
}
void f2(void)
{
	void f3(void);
	f1();
}
void f1(void)
{
	printf("BEN10");
	f3();
}

void f3(void)
{
	printf("DESTINY");
}

the output of the code is
BEN10DESTINYBEN10DESTINY
how can this be coz i'm declaring f1() inside main and calling it in f2(),same for f3().i'm declaring f3() inside f2() and calling it in f1().why is this code not giving any error?
in my opinion as f2() is declared outside of all functions thus it can be used anywhere but f1() and f3() are declared inside specific functions, so they can be used in that function only?
correct me if i'm wrong anywhere.
Thanks

[laserlight]

You can, but typically should not, call functions before declaring them.

[BEN10]

i don't get you

[laserlight]

i don't get you

It's okay, I do not entirely get the implicit function declaration rules for C either, and as far as I know that feature is not part of C99.

Try compiling with the maximum warning level for your compiler and take note of the warning messages generated.

[matsp]

i don't get you

The compiler will allow you to call functions that aren't known (or put another way: without a prototype). But it's recommended that you have prototypes for all functions before using the function. Failure to do this may lead to hard to discover bugs in the code (and certainly will give warnings if warnings are enabled, which is always a good reasin in itself - you should compile your code with warnings).

--
Mats

[BEN10]

The compiler will allow you to call functions that aren't known (or put another way: without a prototype).
Mats

in the same code if i define f2() after f1() then the compiler gives error.

Error	3	error C2371: 'f3' : redefinition; different basic types

also how to set my compiler with maximum warning level.i'm using visual studio 2005.

[Elysia]

Project properties -> C/C++ -> General -> Warning Level -> Set to Level 4.

[zacs7]

> I do not entirely get the implicit function declaration rules for C either
AFAIK, they default to "int xxx()" which is, "int xxx(int arg1, int arg2, ..., int argN)" for C89 at least.

[vart]

"int xxx()" which is, "int xxx(int arg1, int arg2, ..., int argN)" for C89 at least.

Are you sure that arguments should have this type?

The following works fine...

#include <stdio.h>

struct sample { int a; double b;};

int main ()
{
	double x = 0.5;
	int y = 7;
	const char* z = "test";
	struct sample  w = {5,7.8};

	f(x,y,z,w);

	return 0;
}

int f(double x,int y,const char* z,struct sample  w )
{
	printf("x = %.2f, y = %d, z= %s, w = {%d,%.2f}\n", x,y,z,w.a,w.b);
	return 0;
}

[zhankal]

As far as I know ANSI C does not allow such declerations.

here's a code

#include <stdio.h>
void f2(void);
int main(void)
{
	void f1(void);
	f1();
                f2();
	getch();
	return 0;
}
void f2(void)
{
	void f3(void);
	f1();
}
void f1(void)
{
	printf("BEN10");
	f3();
}

void f3(void)
{
	printf("DESTINY");
}

the output of the code is
BEN10DESTINYBEN10DESTINY
how can this be coz i'm declaring f1() inside main and calling it in f2(),same for f3().i'm declaring f3() inside f2() and calling it in f1().why is this code not giving any error?
in my opinion as f2() is declared outside of all functions thus it can be used anywhere but f1() and f3() are declared inside specific functions, so they can be used in that function only?
correct me if i'm wrong anywhere.
Thanks

[itCbitC]

If it's any consolation to you, the code doesn't compile on Unix (at least with the compiler I have).

[BEN10]

so what i understood till now is that any function's scope is from the point it is declared till the end of the file.i mean if i declare any function(say f1()) inside any other function(say f2()) then i can use f1() from the point of declaration to the end of the file whether i call it in some other function's definition.if i call f1() from any other fucntion defined before f2() then it'll be an error.

[laserlight]

so what i understood till now is that any function's scope is from the point it is declared till the end of the file.

Then what about getch()? You call getch() without including the appropriate header that declares it.

zacs7 reminded me about the default int rule, so consider:

#include <stdio.h>

int main(void)
{
    f1();
    f2();
    return 0;
}

int f2(void)
{
    f1();
    return 0;
}

int f1(void)
{
    printf("BEN10");
    f3();
    return 0;
}

int f3(void)
{
    printf("DESTINY");
    return 0;
}

[BEN10]

Then what about getch()? You call getch() without including the appropriate header that declares it.

zacs7 reminded me about the default int rule, so consider:

#include <stdio.h>

int main(void)
{
    f1();
    f2();
    return 0;
}

int f2(void)
{
    f1();
    return 0;
}

int f1(void)
{
    printf("BEN10");
    f3();
    return 0;
}

int f3(void)
{
    printf("DESTINY");
    return 0;
}

yes.i was also about to ask the same question that how the program runs without including the proper header for getch(),which i think is conio.h.and also why you have changed the prototype to int for every function.

[Elysia]

The compiler would assume a default prototype of
int fnc(...)
So no type checking on the arguments and the return type is int.
(If a proper declaration is not found before call.)