Thread: strcat() problems...

Hi all,

My program seems to be giving me an error in the form of a segmentation fault...

Please see my code below with a comment show the point where program execution fails.

Please advise!

Code:

//////////////////////////////////////////////////////////////////////////
// Pre-processor Directives
//////////////////////////////////////////////////////////////////////////

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define NBARGS      2
#define FIFO_FILE   "MYFIFO"
#define MESSAGESIZE 80

//////////////////////////////////////////////////////////////////////////
// Sub Function Prototypes
//////////////////////////////////////////////////////////////////////////

void argumentValidater( int );
char * concatenator( int, char** );

//////////////////////////////////////////////////////////////////////////
// Main Function Implementation
//////////////////////////////////////////////////////////////////////////

int main( int argc, char *argv[] )
{
    argumentValidater( argc );
    char *userString;
    FILE *fp;

    if( ( fp = fopen( FIFO_FILE, "a" ) ) == NULL ) 
    {
        perror( "fopen" );
        exit( EXIT_FAILURE );
    }

    userString = concatenator( argc, argv );
    printf( "\nUSERSTRING: %s", userString );fflush( stdout );

    fputs( userString, fp );
    fclose( fp );
}

//////////////////////////////////////////////////////////////////////////
// Sub Function Implementation
//////////////////////////////////////////////////////////////////////////

void argumentValidater( int argCount )
{
    if( argCount < NBARGS )
        printf( "\nYou must enter a number followed by your string of text!  EXITING...\n" );fflush( stdout );
}

//////////////////////////////////////////////////////////////////////////

char * concatenator( int argCount, char *argVector[] )
{
    int i = 1;
    char *str;
    while( i < ( argCount + 1 ) )
    {
        char *tmpStr;
        tmpStr = argVector[i];
        strcat( str, tmpStr );  /* Problem is here... */
        strcat( str, " " );
        i++;
    }
    strcat( str, "\n" );
    return str;
}

//////////////////////////////////////////////////////////////////////////

Let me ask you a question:
In your function concatenator(), the object str is a pointer. Where does it point to?

That's Schlemiel's string concatenation method. Schlemiel the Painter's algorithm - Wikipedia, the free encyclopedia and Back to Basics - Joel on Software