Please help, why we get wrong element in array,

this is my code :

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

int main(int argc, char **argv)
{
    char db_names[3][36] = {};
    
    strncpy(db_names[0], "6e64e40c-57f6-11ec-91ca-001a6496977d", 36);
    strncpy(db_names[1], "90e852c8-502d-11ec-91ca-001a6496977d", 36);
    strncpy(db_names[2], "28712b0e-57f6-11ec-91ca-001a6496977d", 36);

    printf("index 0 %s\n", db_names[0]);
    printf("index 0 %s\n", db_names[1]); 
    printf("index 0 %s\n", db_names[2]);

    return EXIT_SUCCESS;
} 

print element in array :

index 0 : 6e64e40c-57f6-11ec-91ca-001a6496977d90e852c8-502d-11ec-91ca-001a6496977d28712b0e-57f6-11ec-91ca-001a6496977d

index 1 : 90e852c8-502d-11ec-91ca-001a6496977d28712b0e-57f6-11ec-91ca-001a6496977d

index 2 : 28712b0e-57f6-11ec-91ca-001a6496977d

>Solution :

1. Fix the index in the format string.

2. If you want to print a (non-\0 terminated) character array then you have to use a length modifier %.36s to tell printf() how large the array is:

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

int main(int argc, char *argv[]) {
    char db_names[3][36]={};
    strncpy(db_names[0],"6e64e40c-57f6-11ec-91ca-001a6496977d", 36);
    strncpy(db_names[1], "90e852c8-502d-11ec-91ca-001a6496977d", 36);
    strncpy(db_names[2], "28712b0e-57f6-11ec-91ca-001a6496977d", 36);
    printf("index 0 %.36s\n", db_names[0]);
    printf("index 1 %.36s\n", db_names[1]); 
    printf("index 2 %.36s\n", db_names[2]);
    return EXIT_SUCCESS;
}

1. Alternatively increase the array to 37 elements and copy the terminating \0 so you are operating on strings:

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

int main(int argc, char *argv[]) {
    char db_names[3][37]={};
    strncpy(db_names[0],"6e64e40c-57f6-11ec-91ca-001a6496977d", 37);
    strncpy(db_names[1], "90e852c8-502d-11ec-91ca-001a6496977d", 37);
    strncpy(db_names[2], "28712b0e-57f6-11ec-91ca-001a6496977d", 37);
    printf("index 0 %s\n", db_names[0]);
    printf("index 1 %s\n", db_names[1]);
    printf("index 2 %s\n", db_names[2]);
    return EXIT_SUCCESS;
}

3. (Not fixed) Consider a symbolic constants for the length, and/or sizeof instead of hard-coding 36 or 37.

4. I would initialize the string instead and use a loop to print the result. Used sizeof of the first string; alternatively leave 37 hard-coded or introduce a symbolic constant #define UUID_LEN 36 and use UUID_LEN + 1 when declaring the array.

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

int main(void) {
    char db_names[][sizeof "6e64e40c-57f6-11ec-91ca-001a6496977d"]={
        "6e64e40c-57f6-11ec-91ca-001a6496977d",
        "90e852c8-502d-11ec-91ca-001a6496977d",
        "28712b0e-57f6-11ec-91ca-001a6496977d",
    };
    for(size_t i = 0; i < sizeof db_names / sizeof *db_names; i++)
        printf("index %zu %s\n", i, db_names[i]);
    return EXIT_SUCCESS;
}

Either of the 3 programs will output:

index 0 6e64e40c-57f6-11ec-91ca-001a6496977d
index 1 90e852c8-502d-11ec-91ca-001a6496977d
index 2 28712b0e-57f6-11ec-91ca-001a6496977d