Clash Royale CLAN TAG#URR8PPP

Segmentation Fault when allocating memory to a pointer to pointer variable [C] [closed]

I'm trying to represent an array of strings by using a pointer to pointer. So I've defined char** arr as below:

char** arr

uint8_t lines = getLines();
char** arr = malloc (sizeof (char*) * lines);
// char** arr = malloc (sizeof (char*) * ROWS_COUNT);


In the debug process, the line above will be executed successfully and allocates memory to arr. The problem (and so, the error) issues when trying to allocating enough memory to hold a string within *(arr + 0) as below:

arr

*(arr + 0)

// #define PATH_MAX 4096
*arr = malloc (sizeof (char) * (PATH_MAX + 1));


Runtime Error:

Signal: SIGSEGV (Segmentation fault)


Note: I've used casting operators (the first assignment by char** and the second one by char*). It doesn't work too.

char**

char*

Note: I've used ROW_COUNTS here for the sake of simplicity. In the original code, there is a lines variable which I use instead of ROWS_COUNT. lines contains an uint8_t value. (in my case, 3)

ROW_COUNTS

lines

ROWS_COUNT

lines

uint8_t

3

This question appears to be off-topic. The users who voted to close gave this specific reason:

ROWS_COUNT

PATH_MAX

lines

3

PATH_MAX

malloc

char (*arr)[PATH_MAX+1] = calloc(ROW_COUNT, sizeof *arr);

ROW_COUNT

char

2 Answers
2

You could dynamically allocate memory in single malloc() , Try this code :-

malloc()

char (*arr)[ROWS_COUNT][PATH_MAX + 1] = malloc (sizeof(*arr));


and you could access strings using :-

(*arr)[ index ]


and characters using :-

(*arr)[ row ] [ column ]


Example :-

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define PATH_MAX 4096
#define ROWS_COUNT 500
int main()

char (*arr)[ROWS_COUNT][PATH_MAX + 1] = malloc (sizeof(*arr));
strcpy((*arr)[400],"Hello World");
printf("n String : %s",(*arr)[400]);
printf("n Character : %c",(*arr)[400][2]);



Output :-

String : Hello World
Character : l


ROWS_COUNT

lines

arr

arr

(*arr)

char (*arr)[PATH_MAX+1] = calloc(ROW_COUNT, sizeof *arr);

*

sizeof(*arr)

// #define PATH_MAX 4096
*arr = malloc (sizeof (char) * (PATH_MAX + 1));


I think this line needs to be within a loop of ROWS_COUNT times. So that memory can be allocated for all the rows to be stored.

ROWS_COUNT

Tested on MAC with Xcode (Version 9.3 (9E145)), working fine:

char** arr = (char**) malloc (sizeof (char*) * 1000);
int i = -1;
while(++i < 1000)

*(arr + i) = (char*) malloc (sizeof (char) * (PATH_MAX + 1));



i

1

1001

for(size_t i=0; i<1000; i++) arr[i] = malloc(...);

*(arr + 1000) =