CODEWITHSUNDEEP
c
Archer
Archer

Reputation: 272

Why does each element of my array automatically turn into the last element?

char *string[n];    
for (int i = 0; i < n; i++) {
    char string[60];
    fscanf(fptr, "%s%*[^\n]", string);
    strings[i] = string;
    printf("%s\n", strings[i]);
}
puts("Ended");
for (int i = 0; i < n; i++) {
printf("%s\n", strings[i]);

This is part of my code in C ^. strings[] contains pointers to the first word of each line in the file. So if my file contains: 

ABC 123
DEF 123
GHI 123

I get the following output: 

ABC
DEF 
GHI
Ended
GHI
GHI
GHI

Which means there's nothing wrong with the initialisation. Then what is going on?

Upvotes: 1

Views: 70

Answers (1)

Henry Le Berre
Henry Le Berre

Reputation: 909

When you wrote : 

strings[i]=string

You were not copying the original string into the array because the “string” variable only contains a pointer (memory address) of the stack allocated string. When you go into the next iteration of the for loop, the stack allocated “string” variable gets freed/thrown away.

So your “strings” array contains pointers to unallocated memory. You should use “strcpy” instead. If the size of your “strings” array is not constant, use “malloc” then “strcpy”.

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

int main()
{
    FILE *fptr = fopen("test.txt", "r");
    char strings[10][60];
    int n = 3;
    for (int i = 0; i < n; i++)
    {
        char string[60];
        fscanf(fptr, "%s%*[^\n]", string);
        strcpy(strings[i], string);
        printf("%s\n", strings[i]);
    }
    puts("Ended");
    for (int i = 0; i < n; i++)
    {
         printf("%s\n", strings[i]);
    }
}

Or, simpler:

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

int main()
{
    FILE *fptr = fopen("test.txt", "r");
    char strings[10][60];
    int n = 3;
    for (int i = 0; i < n; i++)
    {
        fscanf(fptr, "%s%*[^\n]", strings[i]);
        printf("%s\n", strings[i]);
    }
    puts("Ended");
    for (int i = 0; i < n; i++)
    {
        printf("%s\n", strings[i]);
    }
}

Upvotes: 3

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