CODEWITHSUNDEEP
cstructcompiler-errors
CIsForCookies
CIsForCookies

Reputation: 12817

unknown type name C vs C++

I tried to create a struct that holds a pointer to it's type:

#include <stdio.h>
struct test{
    test* t;
};
 int main(){
    return 0;
 }

while compiled with gcc, this code produced an error:

:5:2: error: unknown type name 'test'

but while compiled on g++ it went just fine.

So what I want to understand is:

1) What causes this difference? I thought that if gcc uses one-pass compilation and g++ uses multipass that could explain it, but as I understood, this is not true.

2) How can I avoid this error and define a struct with a pointer to it's own type? (I don't want to use a void* or use casting unless there is no other option)

Upvotes: 1

Views: 2123

Answers (3)

haelmic
haelmic

Reputation: 610

You need to typedef struct test test ; before you can use it in that way.

This should work just fine:

#include <stdio.h>
struct test{
   struct test* t;
};
int main(){
    return 0;
}

Or you can try:

#include <stdio.h>
typedef struct test test;
struct test{
   test* t;
};
int main(){
    return 0;
}

Your problem is gcc is a C compiler and takes types literally. If you use a c++ compiler, it may not care. c++ simplifies the types for you C does not. Be careful of this fact. C code will compile in a c++ compiler but c++ will not compile in a c compiler.

Upvotes: 0

Magisch
Magisch

Reputation: 7352

Your syntax is incorrect in "C". You have to use struct <structname>* <varname>; in format.

In c++, you can omit the "struct" in front of it. In C however, you have to write it to define a pointer to your struct.

Fixed code:

#include <stdio.h>
typedef struct test{
   struct test* t;
} test;
 int main(){
    return 0;
 }

Live demo

Upvotes: 2

Viatorus
Viatorus

Reputation: 1903

You have to write struct before test* t to define a pointer to our struct:

struct test* t;

That is one different between C and C++.

Upvotes: 6

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