strcpy giving segmentation fault in c

Question

Hi please help me with this

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

int classmatesize=0;
char **classmate1;
char **classmate2;    

void checkclassmates(){
        int i,j;
        for(i=0;i<classmatesize;i++){
            for(j=i+1;j<classmatesize;j++){
                if(strcmp(classmate1[i],classmate1[j])==0){
                    strcpy(classmate1[classmatesize],classmate2[i]);
                    strcpy(classmate2[classmatesize],classmate2[j]);
                    classmatesize++;
                }else if(strcmp(classmate1[i],classmate2[j])==0){
                    strcpy(classmate1[classmatesize],classmate2[i]);
                    strcpy(classmate2[classmatesize],classmate1[j]);
                    classmatesize++;                
                }else if(strcmp(classmate2[i],classmate2[j])==0){
                    strcpy(classmate1[classmatesize],classmate1[i]);
                    strcpy(classmate2[classmatesize],classmate1[j]);
                    classmatesize++;
                }else if(strcmp(classmate2[i],classmate1[j])==0){
                    strcpy(classmate1[classmatesize],classmate1[i]);
                    strcpy(classmate2[classmatesize],classmate2[j]);
                    classmatesize++;
                }
            }
        }
    }
int main(void) {
    int i;

    classmate1 = malloc(1000 * sizeof(char*));
    for ( i = 0; i < 1000 ; i++)
    classmate1[i] = malloc((1000) * sizeof(char));

    classmate2 = malloc(1000 * sizeof(char*));
    for ( i = 0; i < 1000 ; i++)
    classmate2[i] = malloc((1000) * sizeof(char));


    yyparse();
    checkclassmates();
    print_the_array();
    return 0;
}

my yyparse(); if i print the classmate1 and classmate2 by commenting the checkclassmates function its printing and clasematesize is printing as 7

classmate1
[ sania  pawan  pandu  haldiram  manas  abhi  prince ]
classmate2
[ sam  pandu  madhur  arjun  jyoti  ash  sam ]

proplem is with strcpy only if i comment the strcpy instructions its working fine its giving segmentation fault.
i even tried sprintf instead of strcpy still i cannot figure it out.

Answer 1

My hunch is that the lines

                classmatesize++;

in checkclassmates are the culprits. There are four of them. Since you are are incrementing classmatesize inside the loops, the conditional of the if statements never fail and you end up accessing the arrays out of bounds.

Try removing those lines and see whether the problem is still there.