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hello!
I'm writing a C++ program and the problem I face is when I used typedef for a srtucy as follows:
The error I'm getting from the compiler is:Code:typedef struct{
//declarations
}Foo;
redefinition; different basic types
Maybe is something wrong because Im using typedef in C++?
A simple:
would be equivalent to that C construct.Code:struct Foo
{
//declarations
};
^ this.
I think what you're trying to do is
You're trying to typedef the entire struct name. In C, in order to declare an instance of a struct, you'd have to sayCode:typedef struct Foo
{
} Foo;
So you want to typedef that entire name (struct Foo) into just the name of the struct (Foo)Code:struct Foo bar;
No, that looks right. Are you using Foo somewhere else already?Quote:
Originally Posted by quo
Some all compilers required it this way.
The structure name (often called tag name) and the type name needed to be different on some old compilers.Code:typedef struct Foo_tagname
{
} Foo;
Tim S.
Thank you all very much for your answers!
I tried it the simple way as follows:
and it doesn't return that error any more(there used to be about 300 of them exactly the same)Code:struct Foo{
//declarations
};
but it returns now:
'struct' type redefinition
What is that??:frown:
post the full error message.
it should be something like
Foo:'struct' type redefinition
Kurt
error C2011: 'Foo' : 'struct' type redefinitionQuote:
Originally Posted by ZuK
Post the exact error message and the line of code it says has the error.Quote:
Originally Posted by quo
Then search for another place you define the same identifier.
If the file is a header file (or is included by other files); please confirm it has header guards in it.
Tim S.
That's what I thought.
This is usually an indication that you #include a header multiple times.
That header is propably missing the include guards.
Kurt
all I do in this header file Foo.h is:
nothing else.Code:#include<stdio.h>
#include<iostream>
struct Foo{
//declarations
};
and then i include it wherever is needed..
the error line is line with struct Foo
and gives the error I mentioned above
try include guards like
KurtCode:#ifndef FOO_H_INCLUDED
#define FOO_H_INCLUDED
#include<stdio.h>
#include<iostream>
struct Foo{
//declarations
};
#endif
It doesn't return the mistake now,but could you explain to me what do the guards do exactly?Quote:
Originally Posted by ZuK
Now my Foo.h is included ok in the rest of the code(other .h or .cpp files include Foo.h)?
The problem is that any class or struct may only be defined once in any tranlation unit ( one definition rule ).Quote:
Originally Posted by quo
if you #include a header in other headers then it can happen that a single header is #included more then once. That is not allowed.
Therefore you add includeguards.
The first line ( #ifndef FOO_H_INCLUDED ) tells the preprocessor that the part up to #endif should only be processed if the symbol FOO_H_INCLUDED is not defined.
The next line #defines ths symbol. If the same header is #included another time then the symbol is already defined and your code is skipped.
Google include guards or header guards. I'm shure you will find better and more detailed explainations.
Kurt
Thank you very much!Quote:
Originally Posted by ZuK
I understood the whole thing!
You made it very clear
:)
A #include is equivalent to literally copying and pasting the entire header file into wherever it is included into.
So if you have foo.cpp which includes foo.h and bar.h, and bar.h also includes foo.h, then the resulting source file is compiled with the contents of foo.h pasted into it twice.
The include guards just tell the compiler to ignore any subsequent copies of that header within the resulting source file being compiled. It still copies it in there twice, but the second occurrence is ignored. Some compilers allow you to use "#pragma once" at the top of the file which actually stops the second and subsequent inclusions of the header, but it's not supported on all compilers.
thanks for the explanation:)Quote:
Originally Posted by iMalc