Why can't I print a string point in C?

Asked Apr 08 '17 at 10:22

Active Apr 08 '17 at 10:22

Viewed 33 times

Why I run the code and I just got a segmentation fault?

#include <stdio.h>

int main(void){
    char *string = "hello,world";
    // printf("0x%p\n",string);
    printf("Command:");
    scanf("%s",string);
    printf("%s",string);
    // printf("0x%p\n",&(""));
    // printf("0x%p\n",string);
    return 0;
}

asked Apr 08 '17 at 10:22

Tenma

![runtime](https://lh4.googleusercontent.com/9sauXTPkMb73xz73tss9Ot3Boxk8PTe4n4vMqZsFvoHQSo0d7PWW8HdEe6kcBLLnmv8VzhgECu6i354=w1680-h944-rw) – Tenma Apr 08 '17 at 10:22
String literals can not be changed. – BLUEPIXY Apr 08 '17 at 10:24
But it is char*,not a const char*.I just change its location. – Tenma Apr 08 '17 at 10:26
In this case You should have done like `const char *string = "hello,world";`. because The essence of contents can not be changed – BLUEPIXY Apr 08 '17 at 10:28
See [c11 draft](http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf) **6.4.5 String literals** p7 _It is unspecified whether these arrays are distinct provided their elements have the appropriate values. If the program attempts to modify such an array, the behavior is undefined._ – BLUEPIXY Apr 08 '17 at 10:36
But the code like this,and I can run it in the another machine and my own machine in other day. – Tenma Apr 08 '17 at 10:43
undefined behavior is undefined behavior. It includes both. So Don't expect to work as you wish. – BLUEPIXY Apr 08 '17 at 10:56
So how should I do to fix the code? – Tenma Apr 08 '17 at 11:46
`char command[64] = ""; printf("Command:");fflush(stdout); scanf("%63s", command); printf("%s\n", command);` – BLUEPIXY Apr 08 '17 at 11:49
but if I want to scan a string but it's length is unknown,how to do? – Tenma Apr 08 '17 at 12:04
If available { (1) `char *s = NULL; scanf("%ms", &s);` (2) Use `getline` } . (3) Extend buffer according to reading by using `malloc` and `realloc`. – BLUEPIXY Apr 08 '17 at 12:09
Shall I use %ms? – Tenma Apr 08 '17 at 12:13
It is one of the choices if it is available. That is the simplest. – BLUEPIXY Apr 08 '17 at 12:15
But it doesn't work in my PC – Tenma Apr 08 '17 at 12:15
Then please select (3). – BLUEPIXY Apr 08 '17 at 12:16
So I have to set a length for the string? – Tenma Apr 08 '17 at 13:44
It is necessary to manage the size of used memory and the size of secured memory rather than the current length of the string. – BLUEPIXY Apr 08 '17 at 14:00
Examples of such processing are many on this site and other sites. one of exapmple, [GetString in cs50.c](https://github.com/CoreData/cs50/blob/master/pset1/cs50.c) – BLUEPIXY Apr 08 '17 at 14:03

Why can't I print a string point in C?

0 Answers0