当我们可以直接为它分配一个字符串时，为什么不能将一个字符串复制到“字符指针"中呢? [英] Why Can't we copy a string to Character Pointer WHEN we can assign a string directly to it?

问题描述

此代码产生"p = hello world":

This code produces "p = hello world":

#include "stdio.h"
#include "string.h"

int main(){
    char *p;
    p="hello world";
    printf("p is %s \n",p);
    return 0;
}

但是此代码会产生分段错误:

But this code produces a segmentation fault:

#include "stdio.h"
#include "string.h"

int main() { 
    char *p;
    strcpy(p,"hello");
    printf("p is %s \n",p);
    return 0;
}

并且此代码产生"p = hello"

and this code produces "p = hello"

#include "stdio.h"
#include "string.h"
#include "stdlib.h"
int main() {
  char *p;
  p=(char*)malloc (10);
  strcpy(p,"hello");
  printf("p is %s \n",p);
  return 0;

}

推荐答案

在p="hello world";(此编辑时为第一种情况)的情况下，p初始化为指向 read-仅内存区域，其中包含字符串"hello world"(字符串文字).该只读内存区域是在编译时创建的.

In the case where p="hello world"; (1st case at the time of this edit), p is being initialized to point to a read-only memory region which contains the string "hello world" (string literal). This read-only memory region is created at compile time.

在导致分段错误的情况下(此编辑时为第二种情况)，p未初始化，将任何内容复制到其中将产生不可预测的结果，因为p指向的内存位置不是由代码指定.

In the case that causes the segmentation fault (2nd case at the time of this edit), p is uninitialized and copying anything to it will produce unpredictable results because the location in memory that p is pointing to is not specified by the code.

在将字符串复制到p之前，必须指定p指向的内存.

Before you can copy a string to p, you must specify the memory that p is pointing to.

您可以在堆栈上分配此内存

You can allocate this memory on the stack

char buf[BUFSIZ] = ""; /* local variable */

在堆上

char *buf = malloc(BUFSIZ); /* don't forget to free */

或__DATA段中.

static char buf[BUFSIZ] = ""; /* global variable */

然后可以初始化p指向内存缓冲区.

You can then initialize p to point at the memory buffer.

char *p = buf;

这在概念上类似于初始化p以指向只读内存中的字符串文字.与p指向字符串文字的情况不同，您现在可以将字符串复制到字符指针，因为它不指向只读内存.

This is similar in concept to initializing p to point to the string literal in read-only memory. Unlike the case where p points to the string literal, you can now copy a string to the character pointer as it does not point to read-only memory.

注意:我有意创建了一个单独的缓冲区，并初始化了p指向它，以帮助阐明我的观点.

Note: I intentionally created a separate buffer and initialized p to point to it to help make my point.

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