CODEWITHSUNDEEP
cstructcompiler-errorsheader-files
Balázs Börcsök
Balázs Börcsök

Reputation: 616

Resolving "error: expected identifier" in header file?

I do not understand what identifier is excepted in my dsoptlow.h.

I was practicing creating function declarations in headers. This should swap 2 values using only 2 variables and returning same variables, but with swapped values.

However during compilation this error message is shown and I have no idea what I got wrong or mistyped:

error: expected identifier or '(' before 'int'

Also, if you can give a better version for my function to return multiple values it would be very much appreciated.

And last but not least, does a type defined in a function definition return that type in main function? So does it return a struct I defined as a new type, or integer?

error message during compilation-time

The following code is my header.

#ifndef _dswapoptlow_h
#define _dswapoptlow_h
struct dswap_opt_low(int inp_1; int inp_2;);
#endif

The following code is the function definition.

//dswapoptlow.c src file
#include "dswapoptlow.h"

struct _return{int a;int b;}; //Init a struct named _return for 2 integer variables. 

typedef struct _return _struct;

_struct dswap_opt_low(int inp1, int inp2)
{
    _struct _instance;

    _instance.a=inp1;
    _instance.b=inp2;

    _instance.a=_instance.a+_instance.b;
    _instance.b=_instance.a-_instance.b;
    _instance.a=_instance.a-_instance.b;

    return _instance;
}

Upvotes: 0

Views: 3050

Answers (2)

Rishikesh Raje
Rishikesh Raje

Reputation: 8614

dswap_opt_low in the header is a function declaration. The function returns a struct _return and takes two parameters.

The correct syntax is

struct _return dswap_opt_low(int inp_1, int inp_2);

Also, you can move the definition and typedef of _struct into the header so that this is visible there. Then you can use 

struct _return{int a;int b;}; //Init a struct named _return for 2 integer variables.
typedef struct _return _struct;
_struct dswap_opt_low(int inp_1, int inp_2);

Note that it is a bad design practice to use _ in the first character of an identifier. I would suggest that you change the name and use more descriptive types.

Additional Note - Your function dswap_opt_low returns a local variable _instance. If the returned value is used elsewhere in the program it will result in undefined behaviour and you will get unpredictable results.

Upvotes: 1

David Ranieri
David Ranieri

Reputation: 41046

The message is quite confusing (there should be another error), but your function is returning a struct and the compiler doesn't know the size of this struct

Move these two lines:

struct _return{int a;int b;}; //Init a struct named _return for 2 integer variables. 

typedef struct _return _struct;

from .c to .h

Upvotes: 1

Related Questions