在 C 程序中使用带有指针数组的 strcmp() function

Question

I'm trying to detect duplicate strings in a pointer array. I want to detect if there is any duplication with strcmp() function and want to remove duplications except the first one however the command line is giving error when I add strcmp() function: Segmentation fault (core dumped)

Here is my code; and size is equal to size of the products array.

FILE* temp_file_to_read = fopen("temp.txt", "r");
char temp_line[256];  
char *products[256];
int j = 0;
        while(fgets(temp_line, sizeof(temp_line), temp_file_to_read)){
                //printf("%s", temp_line);
                products[j] = strdup(temp_line);
                printf("%s", products[j]);
                j++;
        }


         for(int i = 0; i< size; i++){
                    for(int j = i+1; j <  size; j++){
                            if(strcmp(products[i], products[j])==0){
                                    printf("%s is exist\n", products[j]);
                            }
                    }
            }

Answer 1

I'm guessing that your file doesn't have 256 products that are exactly 256 characters in length each, so your products array isn't full. So when you do strcmp(products[i], products[j]) , you will at some point be trying to use garbage pointers as if they point to a genuine string, and that's where you're getting a segfault.

There are several things wrong with your code, including

• you probably want to be breaking up your file at new lines, not just every 256 characters (though I could be wrong)
• you should check to make sure you don't try to create more than 256 products, otherwise you'll overflow your array
• when doing the string comparisons, only go as far as the number of products you have, rather than blindly to the end of the array