Why do I get a runtime error when assigning value to a char pointer?

Question

I want to change the contents of the char pointer after allocating dynamic memory, is it possible? If not, why? My program throws a run-time error.

#include <stdio.h>

int main()
{
    char * str = (char *) malloc (10 * sizeof(char));
    str = "Hello";
    str[2] = 'L'; // here the program throws run time error
    printf("%s", str);
    return 0;
}

`str = "Hello";` overwrites the original allocation with a pointer to the charater literal. You cannot write there, hence the error. It's undefined behavior. — πάντα ῥεῖ, Jun 20 '17 at 08:00
@CIsForCookies - So? The tags are for pinpointing a language reference, not increasing exposure for the question. — StoryTeller - Unslander Monica, Jun 20 '17 at 08:00
Possible duplicate of [What is the difference between char s\[\] and char \*s?](https://stackoverflow.com/questions/1704407/what-is-the-difference-between-char-s-and-char-s) — danglingpointer, Jun 20 '17 at 08:01
No , @LethalProgrammer this particular case is not answered in the question https://stackoverflow.com/questions/1704407/what-is-the-difference-between-char-s-and-char-s , you can check. — Dhawal Arora, Jun 20 '17 at 08:18

CIsForCookies · Accepted Answer · 2017-06-20T08:04:16.333

7

When pointing str = "Hello"; you didn't copy the "Hello" into the address pointed by str. Instead, you pointed str to string literal, and modifying it is UB -> run-time-error.

If you want to copy the content of a string Hello to str use strcpy.

As noted by @LethalProgrammer: using char[10] instead of char*would allow you modifying the content

edited Jun 20 '17 at 08:04

answered Jun 20 '17 at 07:58

CIsForCookies

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Surely, @WeatherVane – Dhawal Arora Jun 20 '17 at 08:09

Why do I get a runtime error when assigning value to a char pointer?

1 Answers1