使用字符指针复制字符串时出错

Question

I was implementing string copy function using character pointers but it is showing error. Here is the code:

#include<stdio.h>
#include<string.h>
int main()
{
    char *s="abc";
    char *t;
    while((*s)!='\0')
    {
        *t++=*s++;
    }
    *t='\0';
    printf("%s\n",t);
    return 0;
}

Answer 1

char *t;

There is no memory allocated to your pointer and you are trying to write to it which will lead to undefined behavior.So allocate memory

char *t = malloc(30); /* size of your choice or strlen(s) + 1*/

Once done using the memory free it using

free(t);

Answer 2

This might result in a segmentation fault

The reason being : Just think where is char *t pointing to right now?

Let's have a look at the possibilities :

1.Your char *t is pointing to some memory location which can not be accessed or write-protected;

2.It might work in some cases where your pointer is pointing to a memory location that can be accessed and has required space.The possibilities of that being very small.

So, it's better to use

char *t=NULL;
t=malloc(sizeof(char)*n); //Dynamic approach

here n is the no of bytes you are allocating to t

If you're not comfortable with dynamic memory allocation right now reserve some space for t which you think is enough. This will waste some space though.

After you're done, free the space allocated;

free(t);

Note : Always include <stdlib.h> else malloc will result in a warning.