Function inside function in C

Question

Anybody please elaborate these error:-

void main()
{
    int a=5, b=60, func();

    printf("\nI am in main-1");

    int func(){
        printf("\nI am in funct");
        return 1;
    }
    func();
    printf("\nI am in main-2");
}

The errors I get are:

In function 'main':
Line 8: error: static declaration of 'func' follows non-static declaration
Line 4: error: previous declaration of 'func' was here
Line 3: warning: return type of 'main' is not 'int'

I think C allows nested class because the following code is working fine:

void outerfunc()
{
    int func()
    {
        printf("\nI am in funct");
        return 1;
    }

    func();
}

void main()
{
    printf("\nI am in main-1");

    outerfunc();
    printf("\nI am in main-2");
}

That shows you are not reading a book, a Good Book that is. The Definitive C Book Guide and List - stackoverflow.com/questions/562303/… — Sadique
– Sadique, Commented Sep 6, 2011 at 11:46
@pmg: I always wonder why people get so bothered about void main(). The C standard doesn't prohibit it. — Oliver Charlesworth
– Oliver Charlesworth, Commented Sep 6, 2011 at 11:51
@OP - I think C allows nested class because the following code is working fine - Don't think, start reading buddy :-) - stackoverflow.com/questions/2608158/nested-function-in-c — Sadique
– Sadique, Commented Sep 6, 2011 at 11:57

Nordic Mainframe · Accepted Answer · 2011-09-06 12:06:17Z

14

You are using an extension of the GNU C Compiler which allows the declarations of nested functions. The error comes from the fact, that forward declarations of nested functions under GCC's extension need to be prepended with the auto keyword.

int a=20,b=11;
int main()
{
  int a=5, b=60; 
  auto int func(); // <--------- here
  func(); // <- call it
  printf("\nI am in main-1");

  int func(){
  printf("\nI am in funct");
  return 1;
  }

printf("\nI am in main-2");
 return 0;
}

See http://gcc.gnu.org/onlinedocs/gcc/Nested-Functions.html for more details.

edited Sep 6, 2011 at 12:06

answered Sep 6, 2011 at 11:49

Nordic Mainframe

28.9k10 gold badges69 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Mu Qiao · Accepted Answer · 2011-09-06 11:43:38Z

9

ANSI C doesn't allow nested function definition. And your main function should return int.

answered Sep 6, 2011 at 11:43

Mu Qiao

7,1271 gold badge34 silver badges35 bronze badges

5 Comments

Justin Over a year ago

Yes it does (at least as a GCC "extension" of C)

Nordic Mainframe Over a year ago

Apparently (from the error messages one can tell), he is using gcc which in fact has nested functions!

Mu Qiao Over a year ago

@Justin ok, to be more accurate, ANSI C

Justin Over a year ago

@Oli Fair enough, but the poster said "C", not "ANSI C".

Nordic Mainframe Over a year ago

@Oli: OP didn't say that he uses ANSI-C

iammilind · Accepted Answer · 2011-09-06 11:44:52Z

1

Nested functions are not allowed in standard C/C++. Simply (forward) declare the func() inside main() if you want to define it later on.

int main()
{
  int a=5, b=60, func();

printf("\nI am in main-1");

  int func();  // <---- declare inside main()

printf("\nI am in main-2");
}


int func(){    // <---- define later
  printf("\nI am in funct");
  return 1;
}

answered Sep 6, 2011 at 11:44

iammilind

70.5k39 gold badges188 silver badges364 bronze badges

Comments

Justin · Accepted Answer · 2011-09-06 12:01:17Z

What you are taking about is a GCC specific feature, its never been a "proper" C feature (i.e. part of the ANSI C specification).

If you want to use this feature then I believe what you are after is this:

#include <stdio.h>

int a = 20, b = 11;

int main( int argc, char* argv[] )
{
    int a = 5, b = 60;
    auto int func( void );

    printf("\nI am in main-1");

    int func( void )
    {
        printf("\nI am in funct");
        return 1;
    }

    printf("\nI am in main-2");
    return func();
}

The reason why your previous code didn't work is because nested functions have no linkage:

A nested function always has no linkage. Declaring one with extern or static is erroneous. If you need to declare the nested function before its definition, use auto (which is otherwise meaningless for function declarations).

The above sample uses the auto keyword thusly. I've also taken the liberty of fixing your main declaration :-)

John Bode · Accepted Answer · 2011-09-06 14:23:58Z

1

Nested functions are a gcc-specific extension; they are not universally supported.

As far as the warning about main, the standard signatures for main are

int main(void)
int main(int argc, char **argv) // or equivalent

An implementation may provide additional signatures (some compilers allow a third parameter for environment variables), but those additional signatures must be documented by the implementation; IOW, void main() is only a valid signature for main if your compiler documentation explicitly lists it as such.

When in doubt, use one of the standard signatures above.

answered Sep 6, 2011 at 14:23

John Bode

125k19 gold badges130 silver badges211 bronze badges

Comments

Daniel A. White · Accepted Answer · 2011-09-06 11:44:24Z

0

You haven't defined func before calling it.
Relates back to the original line.
You aren't returning int.

answered Sep 6, 2011 at 11:44

Daniel A. White

192k49 gold badges389 silver badges473 bronze badges

Comments

Diego Sevilla · Accepted Answer · 2011-09-06 11:45:58Z

0

It works if you remove the declaration of func() in the int variable declarations.

answered Sep 6, 2011 at 11:45

Diego Sevilla

29.1k4 gold badges62 silver badges91 bronze badges

Comments

DaeDaLuS_015 · Accepted Answer · 2011-09-06 11:48:54Z

0

C++ does not allow functions to be included inside other functions.

Attempting to do so in VS 2010 gives:

'funct' : local function definitions are illegal

You need to move that function and it's declaration outside of main.

answered Sep 6, 2011 at 11:48

DaeDaLuS_015

1105 bronze badges

Collectives™ on Stack Overflow

Function inside function in C

8 Answers 8

Comments

5 Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

8 Answers 8

Comments

5 Comments

Comments

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related