How to fix it? CRT detected that the application wrote to memory after end of heap buffer

Question

im making a pointer array to strings and this issue happened

Is there anythings wrong with my code

char x[50];
int num = 0;
int i = 0;
char* arrs;
printf("Enter number");
scanf("%d", &num);
arrs = (char*)malloc(sizeof(char) * num);
getchar();
for (i = 0; i < num; i++)
{
    printf("Enter str number %d\n" , i);
    fgets(x, 50, stdin);
    *(arrs+i) = (char)malloc(sizeof(char) * strlen(x));
    strcpy((arrs+ i), x);
}

*im making a pointer array to strings and this issue happened* `char* arrs;` this is not a pointer array. It is a pointer. — wildplasser, Apr 13 '16 at 11:36
Seriously, this [error would be more obvious if you **didn't** cast the return value of `malloc'](http://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc). — Antti Haapala -- Слава Україні, Apr 13 '16 at 11:37
Sorry but your question is unanswerable unless you explain **what the code is supposed to do when it is working correctly**. — Antti Haapala -- Слава Україні, Apr 13 '16 at 11:39

nalzok · Answer 1 · 2016-04-13T12:11:46.470

0

arrs should be a "pointer to pointer to char", rather than simply a "pointer to char":

char x[50];
int num = 0;
int i = 0;
char **arrs;                            // <--- pointer to pointer
printf("Enter number:");
scanf("%d", &num);
arrs = malloc(sizeof (char *) * num);   // <--- sizeof (char *)
getchar();
for (i = 0; i < num; i++)
{
    printf("Entered str number %d\n", i);
    fgets(x, 50, stdin);
    arrs[i] = malloc(strlen(x) + 1);    // <--- +1 for the terminating '\0'
    strcpy(arrs[i], x);                 // <--- arrs[i] is a char *
}

// Do something

for (i = 0; i < num; i++)
{
    free(arrs[i]);
}
free(arrs);

edited Apr 13 '16 at 12:11

answered Apr 13 '16 at 11:39

nalzok

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I have noticed the issue happens because the free and not because the code here but thanks too you helped me understand some stuff! What is the proper way to free it? – user23634623 Apr 13 '16 at 11:53
@uSEwrasd Answer improved – nalzok Apr 13 '16 at 11:58
`arrs[i] = malloc(strlen(x));` -> `arrs[i] = malloc(strlen(x) + 1);` – DaV Apr 13 '16 at 12:02
@sunqingyao for some reason for (i = 0; i < num; i++) { free(friends[i]); } this part causes it – user23634623 Apr 13 '16 at 12:06
@uSEwrasd I cannot understand you: What's `friends[i]`? It'll be helpful if you can provide the relevant code. – nalzok Apr 13 '16 at 12:13
@sunqingyao its a string , (its the same code you wrote here) – user23634623 Apr 13 '16 at 12:26
@uSEwrasd Can you show me the complete error message? – nalzok Apr 13 '16 at 12:30

score 0 · Answer 2 · answered Apr 13 '16 at 11:44

0

The problem is your are allocating memory for an array of chars not an array of String, this is char pointers. Just change sizeof(char) by sizeof(char *)

answered Apr 13 '16 at 11:44

Nevado

162
7

How to fix it? CRT detected that the application wrote to memory after end of heap buffer

2 Answers2