function declared inside other

here's a code

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

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

i don't get you

Quote:

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Originally Posted by BEN10

i don't get you

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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.

Quote:

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Originally Posted by BEN10

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

Quote:

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Originally Posted by matsp

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

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

Code:

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

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

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

> 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.

Quote:

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Originally Posted by zacs7

"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...

Code:

---

#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;
}

---

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

Quote:

---

Originally Posted by BEN10

here's a code

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

---

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

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.

Quote:

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Originally Posted by 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.

---

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:

Code:

---

#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;
}

---

Quote:

---

Originally Posted by laserlight

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:

Code:

---

#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.

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.)

Quote:

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Originally Posted by 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.)

---

ok. the compiler only assumes default type int when no declaration is found prior to calling and.is that what u mean?and what about the arguments listed in the call?

Quote:

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Originally Posted by 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.

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yep! that's it

Quote:

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Originally Posted by BEN10

ok. the compiler only assumes default type int when no declaration is found prior to calling and.is that what u mean?

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Yes.

Quote:

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and what about the arguments listed in the call?

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Nothing. The compiler assumes that the prototype takes an infinite number of arguments, such as:
int myfunction();

Quote:

---

Originally Posted by BEN10

ok. the compiler only assumes default type int when no declaration is found prior to calling and.is that what u mean?and what about the arguments listed in the call?

---

they are compared 1-to-1 with the function parameters

Quote:

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Originally Posted by Elysia

Yes.



Nothing. The compiler assumes that the prototype takes an infinite number of arguments, such as:
int myfunction();

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hmm...that's why we should explicitly write int myfunc(void) to make the function not take any arguments.and is this(compiler's assunption) the reason for the compiler not showing any error while i used getch() without its proper header.

Yes, you need to do that in prototypes, otherwise the compiler assumes it takes an infinite number of arguments.

Quote:

---

Originally Posted by BEN10

hmm...that's why we should explicitly write int myfunc(void) to make the function not take any arguments.and is this(compiler's assunption) the reason for the compiler not showing any error while i used getch() without its proper header.

---

If you enable warnings, which is generally a good idea, it will warn you for not having a prototype.

--
Mats