Pointer issue not solved

Question

In the below code, the file test.txt has the following data :

192.168.1.1-90    
192.168.2.2-80    

The output of this is not as expected. I expect the output to be

192.168.1.1    
90     
192.168.2.2   
80

The current output is

192.168.2.2    
80     
192.168.2.2     
80

I know that the pointer of str is pointing to the same address in the second iteration as well.

Im just not able to the problem. Any help would be appreciated.

#include <string.h> 
#include <stdio.h>
#include <stdlib.h>
int main() {
  FILE * fp;
  char * result[10][4];
  int i = 0;
  const char s[2] = "-";
  char temp[50];
  char * value, str[128], * string, t[20], x[29] = "192.168.2.2";
  fp = fopen("test.txt", "r");
  if (fp == NULL)
    printf("File doesn't exist\n");
  else {
    while (!feof(fp)) {

      if (fgets(str, sizeof(str), fp)) {

        /* get the first value */
        value = strtok(str, s);

        result[i][0] = value;
        printf("IP : %s\n", result[i][0]); //to be removed after testing


        /* get second value */
        value = strtok(NULL, s);

        result[i][1] = value;
        printf("PORT : %s\n", result[i][1]); //to be removed after testing
        i++;
      }
    }
    for (int k = 0; k < 2; k++) {
      for (int j = 0; j < 2; j++) {
        printf("\n%s\n", result[k][j]);
      }
    }

  }
  return (0);
}

Answer 1

I suggest using malloc for allocating space for each ip and port, and freeing them at the end with free. Additionally, a struct might be handy here, if you have bigger text files in the future that you want to use.

The code:

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

#define COLS 2
#define MAXCHAR 10
#define BUFFSIZE 128

void exit_if_null(void *ptr, const char *msg);

int
main(void) {
    FILE *filename;
    char *result[COLS][MAXCHAR+1];
    char buffer[BUFFSIZE];
    char *ip, *port;
    int row, i = 0;

    filename = fopen("ips.txt", "r");

    if (filename == NULL) {
        fprintf(stderr, "%s\n", "Error reading file!\n");
        exit(EXIT_FAILURE);
    } else {
        while (fgets(buffer, BUFFSIZE, filename) != NULL && i < 2) {
            ip = strtok(buffer, "-");
            port = strtok(NULL, "\n");

            result[i][0] = malloc(strlen(ip)+1);
            exit_if_null(result[i][0], "Initial Allocation");

            result[i][1] = malloc(strlen(port)+1);
            exit_if_null(result[i][1], "Initial Allocation");

            strcpy(result[i][0], ip);
            strcpy(result[i][1], port);

            i++;
        }
    }

    for (row = 0; row < i; row++) {
        printf("%s\n", result[row][0]);
        printf("%s\n", result[row][1]);

        free(result[row][0]);
        free(result[row][1]);

        result[row][0] = NULL;
        result[row][1] = NULL;
    }

    return 0;
}

void
exit_if_null(void *ptr, const char *msg) {
    if (!ptr) {
        printf("Unexpected null pointer: %s\n", msg);
        exit(EXIT_FAILURE);
    }
}

Answer 2

What you are doing wrong is that you are assigning "value" pointer to elements of "result" array. In your implementation, all the elements of "result" just mirror the value of "value" pointer. Therefore, when you change the value of "value", you also change all the "result" elements.

Because of that, you should use strcpy function after allocating memory for the specific "result" element.

value = strtok(str, s);
result[i][0]=malloc(strlen(value) + 1);
strcpy(result[i][0], value);

Answer 3

I propose like this:

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

enum { IP = 0, PORT = 1};

int main(void){
    FILE *fp;
    char result[2][2][16];//2 lines, 2 kinds, 16:XXX.XXX.XXX.XXX+NUL
    const char *s = "-";//delimiter
    char *value, line[128];
    int i=0;

    fp = fopen("test.txt", "r");
    if (fp == NULL) {
        printf("File doesn't exist\n");
        exit(EXIT_FAILURE);
    }
    while(i < 2 && fgets(line, sizeof(line), fp)){
        value = strtok(line, s);
        strcpy(result[i][IP], value);
        printf("IP : %s\n",result[i][IP]);

        value = strtok(NULL, s);
        strcpy(result[i][PORT], value);
        printf("PORT : %s\n",result[i][PORT]);
        i++;
    }
    puts("");
    for (int k=0;k<2;k++){
        for (int j=0;j<2;j++){
            printf("%s\n",result[k][j]);
        }
    }
    fclose(fp);

    return 0;
}

Answer 4

When you want to keep-copy strings you have to use the function strcpy()

Instead of result[i][x] = value you should do the following

strcpy(result[i][x], value);

Edit: Before the strcpy you have to use malloc to allocate memory for the result[i][x] string. eg:

result[i][0] = malloc(10 * sizeof(char));