Forward declaration of function messes up, saying args are undeclared identifiers

Question

This is my code:

mainheader.h

void displaygrid(int (* _grid)[10][10] , string msg );

something.cpp

#include <string>
#include "mainheader.h"

void displaygrid(int (* _grid)[10][10], string msg = "" )
{
   //body goes here
}

Compiler says at line of forward declaration in header:

_grid and string are undeclared identifiers

however since its just prototype, it shouldnt be worried about existence of _grid, right ?

Also, header is included after the string , but it doesnt know about string as well. It looks like its trying to call function instead of forward declaring. What's wrong?

When posting a question about compiler or linker errors, it is always helpful to include the actual errors. Not edited or shorted down but complete and unedited. — Some programmer dude, Feb 05 '13 at 16:33
Also, ALWAYS have your default values in the header file (and _NOT_ in the implementation - otherwise, some smart guy will change one, and not the other, and either it won't work as expected, or someone else will think "What the **** does this value come from". Default arguments are added by the compiler when it compiles the function - which typically happens from the header file. — Mats Petersson, Feb 05 '13 at 16:36

score 4 · Accepted Answer · answered Feb 05 '13 at 16:31

4

For string you have to use std::string.

answered Feb 05 '13 at 16:31

Some programmer dude

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score 1 · Answer 2 · answered Feb 05 '13 at 16:35

1

It needs to know about __grid in the header as well as string - forward declare or not. You need to at least place a struct __grid; somewhere above it or the likes so it has some sort of clue of what it is. Same for string...

answered Feb 05 '13 at 16:35

Michael Dorgan

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`_grid` is a name of a variable, not a struct – Dan F Feb 05 '13 at 16:46

score 1 · Answer 3 · edited May 23 '17 at 11:56

1

You need to #include <string> in your mainheader.h and refer to string as std::string. You also need to include whatever is necessary to get _grid:

//mainheader.h
#include <string>
void displaygrid(int (* _grid)[10][10] , std::string msg );

Forward declaration of function messes up, saying args are undeclared identifiers

4 Answers4