I am trying to write a program which dynamically allocates memory for a certain string, and then i want to store 5 different values of the same string within the memory so i can access it later. Some of the code ive written is

#include <stdio.h>
#include <inttypes.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>
#include <string.h>

int main( int argc, char *argv[] )  
{
   int c;
   int i = 0;
   int k = 0;
   
   int d = 43;
   char *data = (char*) malloc(5 * 40 * sizeof(int));
   char buf[40];
   
   while (i<5){
    time_t t = time(NULL);
    struct tm tm = *localtime(&t);
    //printf("%d-d-d d:d:d ",tm.tm_mon   1, tm.tm_mday,tm.tm_year   1900, tm.tm_hour, tm.tm_min, tm.tm_sec); // 28
    //printf("%ld\n",sizeof("%d-d-d d:d:d"));
    //printf("%d: %f\n", d, d/58.0 ); // 8
    sprintf(buf,"%d-d-d d:d:d %d: %f\n", tm.tm_mon   1, tm.tm_mday,tm.tm_year   1900, tm.tm_hour, tm.tm_min, tm.tm_sec,d, d/58.0);
    //printf("%ld\n",sizeof("%d: %f\n"));
    if (k < (5*40)){
        int j = 0;
        while (j<40){
        *(data   j   k) = buf[j]; 
        j  ;
        }
        k =40;
    }
    printf("%s",data);
    i  ;
    sleep(1);
   }
   printf("Finished");
   // printf("%d",*(data));
    
}

So, at each iteration of the loop the 'buf' variable stores a different datetime and then i copy it to the allocated memory. So in theory, i have 5 different datetime buffer stored in the allocated memory. When i continue with the compilation of this code,data only prints one datetime and not the rest. If im understanding it correctly, its because im only accessing the first memory location? Am i doing something wrong? If so, how would i go about storing 5 different date time strings and then accessing them all

CodePudding user response：

Assuming you don't know the individual string lengths until run-time, then you'd allocate this as char* data[5]; and assign each data[i] to point at malloc(strlen(some_string) 1). Then strcpy into this allocated space. You'll need a free() call per malloc call.

Or if you for some strange reason just want to dynamically allocate a 2D array with dimensions 5x40, then that would be:

char (*data)[40] = malloc( sizeof(char[5][40]) );
...
data[i][j] = some_character;
...
free(data);