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Extern struct

Hi all:

I am trying to use data from a structure in different modules ( extern struct), with no success. Here's what I am doing:

main.c:

#include "main.h"
struct my_struct new_struct;

void main(void)
{
   new_struct.a = 4321;
}

file1.c:

#include "main.h"
extern my_struct new_struct;


void test()
{
    new_struct.a = 1234;
}

main.h:


struct my_struct
{
    int a;
    int b;
}


The compiler tells me that left side of . requires struct or union....
As I have followed previous threads about this, I see this guidelines are correct. What can be wrong here ?
I am using c51 ver 8.12

Thanks in advance

Juan

Parents

0 ashley madison over 16 years ago in reply to Juan Velasquez

With new_struct's declaration in file1.c lacking the keyword 'struct', it is not a structure declaration, it's an 'int' declaration.
C51 produced an error message telling you what types the '.' operator works with (none are 'int').
You used Visual C++ to compile your example without error.
Successful compilation with Visual C++ led you to believe the problem was C51's bug rather than it a problem with your declaration.

Some observations:

There is no setting to have C51 accept valid C, but C that you did not intend.
Certainly it would be less effort to have carefully examined the error message and correct the declaration by inserting "struct" between "extern" and "my_struct" than to try to find a means of having C51 change its concept of standard C's "default int" behavior.
If you are going to use a C++ compiler to validate C code, you should be investigating options for it, not C51 -- options that put in a strictly C-conforming mode.
Other options include using lint.

For example, I've pasted the following into Gimpel's online lint gimpel-online.com/.../genPage.py :

struct my_struct
{
    int a;
    int b;
};

extern my_struct new_struct;

void test()
{
    new_struct.a = 1234;
}

With these results:

FlexeLint for C/C++ (Unix) Vers. 9.00c, Copyright Gimpel Software 1985-2009

--- Module:   diy.c (C)
                 _
extern my_struct new_struct;
diy.c  10  Info 808: No explicit type given symbol 'my_struct',
    int assumed
diy.c  10  Error 10: Expecting ';'
diy.c  10  Error 19: Useless Declaration
    _
    new_struct.a = 1234;
diy.c  14  Error 40: Undeclared identifier 'new_struct'
diy.c  14  Error 10: Expecting a structure or union
diy.c  14  Error 40: Undeclared identifier 'a'
diy.c  14  Error 63: Expected an lvalue

    --- Wrap-up for Module: diy.c

Info 753: local struct 'my_struct' (line 4, file diy.c) not
    referenced
diy.c  4  Info 830: Location cited in prior message
Info 754: local structure member 'my_struct::a' (line 6, file
    diy.c) not referenced
diy.c  6  Info 830: Location cited in prior message
Info 754: local structure member 'my_struct::b' (line 7, file
    diy.c) not referenced
diy.c  7  Info 830: Location cited in prior message

--- Global Wrap-up

Info 714: Symbol 'test(void)' (line 12, file diy.c) not
    referenced
diy.c  12  Info 830: Location cited in prior message

Reply

0 ashley madison over 16 years ago in reply to Juan Velasquez

With new_struct's declaration in file1.c lacking the keyword 'struct', it is not a structure declaration, it's an 'int' declaration.
C51 produced an error message telling you what types the '.' operator works with (none are 'int').
You used Visual C++ to compile your example without error.
Successful compilation with Visual C++ led you to believe the problem was C51's bug rather than it a problem with your declaration.

Some observations:

There is no setting to have C51 accept valid C, but C that you did not intend.
Certainly it would be less effort to have carefully examined the error message and correct the declaration by inserting "struct" between "extern" and "my_struct" than to try to find a means of having C51 change its concept of standard C's "default int" behavior.
If you are going to use a C++ compiler to validate C code, you should be investigating options for it, not C51 -- options that put in a strictly C-conforming mode.
Other options include using lint.

For example, I've pasted the following into Gimpel's online lint gimpel-online.com/.../genPage.py :

struct my_struct
{
    int a;
    int b;
};

extern my_struct new_struct;

void test()
{
    new_struct.a = 1234;
}

With these results:

FlexeLint for C/C++ (Unix) Vers. 9.00c, Copyright Gimpel Software 1985-2009

--- Module:   diy.c (C)
                 _
extern my_struct new_struct;
diy.c  10  Info 808: No explicit type given symbol 'my_struct',
    int assumed
diy.c  10  Error 10: Expecting ';'
diy.c  10  Error 19: Useless Declaration
    _
    new_struct.a = 1234;
diy.c  14  Error 40: Undeclared identifier 'new_struct'
diy.c  14  Error 10: Expecting a structure or union
diy.c  14  Error 40: Undeclared identifier 'a'
diy.c  14  Error 63: Expected an lvalue

    --- Wrap-up for Module: diy.c

Info 753: local struct 'my_struct' (line 4, file diy.c) not
    referenced
diy.c  4  Info 830: Location cited in prior message
Info 754: local structure member 'my_struct::a' (line 6, file
    diy.c) not referenced
diy.c  6  Info 830: Location cited in prior message
Info 754: local structure member 'my_struct::b' (line 7, file
    diy.c) not referenced
diy.c  7  Info 830: Location cited in prior message

--- Global Wrap-up

Info 714: Symbol 'test(void)' (line 12, file diy.c) not
    referenced
diy.c  12  Info 830: Location cited in prior message

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