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Oct 29th, 2007

Problem when passing a structure containing an array of 2D-chars array to a function

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Hello.

Here's my structure:

C Syntax (Toggle Plain Text)
 
struct settings {
char setting[40][255];
};
struct settings {
char setting[40][255];
};

Here's the function that is supposed to take a pointer to an instance of the above structure and modify it :

C Syntax (Toggle Plain Text)
void changeSetting(struct settings *tempSettings, char *newValue, int indexValue) 
{
        if( indexValue<40){   // to avoid out of boundary problems
        // according to the debugger, the program crashes in this line :	
        strcpy(tempSettings->setting[indexValue], newValue)};  
}
void changeSetting(struct settings *tempSettings, char *newValue, int indexValue) 
{
        if( indexValue<40){   // to avoid out of boundary problems
        // according to the debugger, the program crashes in this line :	
        strcpy(tempSettings->setting[indexValue], newValue)};  
}

Now, here is my main :

C Syntax (Toggle Plain Text)
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <main.h> //contains the struct + changeSetting function
 
int main()
{
struct settings MySettings;   
changeSetting(&MySettings, "penguin", 0);  
 
// supposetly the line above will assign "penguin" to MySettings.setting[0]
// but program crashes
 
return 0; // literally *sigh* 
}
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <main.h> //contains the struct + changeSetting function

int main()
{
struct settings MySettings;   
changeSetting(&MySettings, "penguin", 0);  

// supposetly the line above will assign "penguin" to MySettings.setting[0]
// but program crashes

return 0; // literally *sigh* 
}

I've been debugging for about 13 hours now, not to mention Googling / looking in
mailinglists .

I think it's something to do with the last line in changeSetting function, but I can't point where exactly! Am I supposed to add brackets somewhere ? ( i.e. (*tempSettings)->etc ) or is the problem with me using "->" instead of "." to access the members ? or is it some problem / limitation with C pointers/structures/2D-arrays-in-structures ?

Any help / guidance would be appreciated =)

Thanks in advance,
Axel

P.S: forgot to mention, something identical to this was posted here 2 years ago by another user ( found it when I searched here ). Unfortunately, there was no answer =\
Link : http://www.daniweb.com/forums/thread28036.html

Last edited by the.alchemist; Oct 29th, 2007 at 10:36 pm.

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the.alchemist

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Oct 29th, 2007

Re: Problem when passing a structure containing an array of 2D-chars array to a function

P.P.S: Using MSVC7.1 compiler

the.alchemist

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Oct 30th, 2007

Re: Problem when passing a structure containing an array of 2D-chars array to a funct

One of the lovely things about C...

Check line 5 of changeSetting(): you've got the ; on the wrong side of the }.

Every single statement in C must be terminated by a semi-colon. It's the little things that get you...

Duoas

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Re: Problem when passing a structure containing an array of 2D-chars array to a funct

There's nothing wrong with your code except:

(Toggle Plain Text)

strcpy(tempSettings->setting[indexValue], newValue)};

that semicolon needs to be before the closing }

Quote ...

I think it's something to do with the last line in changeSetting function, but I can't point where exactly! Am I supposed to add brackets somewhere ? ( i.e. (*tempSettings)->etc ) or is the problem with me using "->" instead of "." to access the members ? or is it some problem / limitation with C pointers/structures/2D-arrays-in-structures ?

you can do (*tempSettings).setting[indexValue] or what you just wrote tempSettings->setting[indexValue]. Both are the same.

Aia

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Nearly a Posting Maven

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Oct 30th, 2007

Re: Problem when passing a structure containing an array of 2D-chars array to a funct

Assuming the ; is a typo (it won't even compile), then it seems fine here (cygwin/gcc)

C Syntax (Toggle Plain Text)
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
 
struct settings {
    char setting[40][255];
};
 
void changeSetting(struct settings *tempSettings, char *newValue,
                   int indexValue)
{
    if (indexValue < 40) {
        strcpy(tempSettings->setting[indexValue], newValue);
    }
}
 
int main()
{
    struct settings MySettings;
    changeSetting(&MySettings, "penguin", 0);
    printf( "Penguin Power=%s\n", MySettings.setting[0] );
    return 0;
}
 
$ gcc -W -Wall -ansi -pedantic foo.c
$ ./a.exe
Penguin Power=penguin
#include <stdio.h>
#include <string.h>
#include <stdlib.h>

struct settings {
    char setting[40][255];
};

void changeSetting(struct settings *tempSettings, char *newValue,
                   int indexValue)
{
    if (indexValue < 40) {
        strcpy(tempSettings->setting[indexValue], newValue);
    }
}

int main()
{
    struct settings MySettings;
    changeSetting(&MySettings, "penguin", 0);
    printf( "Penguin Power=%s\n", MySettings.setting[0] );
    return 0;
}

$ gcc -W -Wall -ansi -pedantic foo.c
$ ./a.exe
Penguin Power=penguin

Your struct is about 10K in size. This shouldn't be a problem if your compiler is a 32-bit compiler, but some old 16-bit compilers used very small (like 3K) stack sizes, and this would obviously blow that right out of the water.

Salem

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