参见C常见问题，问题1.32

Q: What is the difference between these initializations? char a[] = "string literal"; char *p = "string literal"; My program crashes if I try to assign a new value to p[i]. A: A string literal (the formal term for a double-quoted string in C source) can be used in two slightly different ways: As the initializer for an array of char, as in the declaration of char a[] , it specifies the initial values of the characters in that array (and, if necessary, its size). Anywhere else, it turns into an unnamed, static array of characters, and this unnamed array may be stored in read-only memory, and which therefore cannot necessarily be modified. In an expression context, the array is converted at once to a pointer, as usual (see section 6), so the second declaration initializes p to point to the unnamed array's first element. Some compilers have a switch controlling whether string literals are writable or not (for compiling old code), and some may have options to cause string literals to be formally treated as arrays of const char (for better error catching).

不变的记忆

由于字符串字面量在设计上是只读的，所以它们存储在内存的Constant部分。存储在那里的数据是不可变的，即不能被更改。因此，在C代码中定义的所有字符串字面值在这里都获得一个只读内存地址。

栈内存

内存的堆栈部分是存放局部变量地址的地方，例如，函数中定义的变量。

正如@matli的回答所暗示的，有两种方法来处理这些常量字符串。

1. 指向字符串字面量的指针

当我们定义指向字符串字面量的指针时，我们是在Stack内存中创建一个指针变量。它指向底层字符串字面值所在的只读地址。

#include <stdio.h>

int main(void) {
  char *s = "hello";
  printf("%p\n", &s);  // Prints a read-only address, e.g. 0x7ffc8e224620
  return 0;
}

如果我们试图通过插入来修改s

s[0] = 'H';

我们得到一个分割错误(核心转储)。我们试图访问不应该访问的内存。我们正在尝试修改只读地址0x7ffc8e224620的值。

2. 字符数组

对于示例而言，假设存储在常量内存中的字符串字面值“Hello”具有与上述地址相同的只读内存地址0x7ffc8e224620。

#include <stdio.h>

int main(void) {
  // We create an array from a string literal with address 0x7ffc8e224620.
  // C initializes an array variable in the stack, let's give it address
  // 0x7ffc7a9a9db2.
  // C then copies the read-only value from 0x7ffc8e224620 into 
  // 0x7ffc7a9a9db2 to give us a local copy we can mutate.
  char a[] = "hello";

  // We can now mutate the local copy
  a[0] = 'H';

  printf("%p\n", &a);  // Prints the Stack address, e.g. 0x7ffc7a9a9db2
  printf("%s\n", a);   // Prints "Hello"

  return 0;
}

注意:当使用指针指向字符串字面量时，如1。，最好的做法是使用const关键字，如const *s = "hello"。这样可读性更强，并且当它被违反时，编译器将提供更好的帮助。然后它将抛出类似error:分配只读位置' *s '的错误，而不是seg错误。编辑器中的linter也可能在手动编译代码之前发现错误。

// create a string constant like this - will be read only
char *str_p;
str_p = "String constant";

// create an array of characters like this 
char *arr_p;
char arr[] = "String in an array";
arr_p = &arr[0];

// now we try to change a character in the array first, this will work
*arr_p = 'E';

// lets try to change the first character of the string contant
*str_p = 'G'; // this will result in a segmentation fault. Comment it out to work.


/*-----------------------------------------------------------------------------
 *  String constants can't be modified. A segmentation fault is the result,
 *  because most operating systems will not allow a write
 *  operation on read only memory.
 *-----------------------------------------------------------------------------*/

//print both strings to see if they have changed
printf("%s\n", str_p); //print the string without a variable
printf("%s\n", arr_p); //print the string, which is in an array. 

要理解这个错误或问题，您应该首先了解指针和数组的差异b/w 所以在这里，我首先要解释一下它们的区别

字符串数组

 char strarray[] = "hello";

在存储器数组中存储的是连续存储器单元，存储为[h][e][l][l][o][\0] =>[]是1个char字节大小的存储器单元，而这个连续存储器单元可以通过名为strarray的名称在这里访问。这里string数组strarray本身包含初始化的所有字符串。在这种情况下，"hello" 因此，我们可以通过访问每个字符的索引值来轻松地更改其内存内容

`strarray[0]='m'` it access character at index 0 which is 'h'in strarray

它的值变成了m所以strarray的值变成了mello;

这里需要注意的一点是，我们可以通过一个字符一个字符地改变字符串数组的内容，但不能像strarray="new string"这样直接初始化其他字符串，这是无效的

指针

我们都知道指针指向内存中的内存位置， 未初始化的指针指向随机内存位置，初始化后指向特定内存位置

char *ptr = "hello";

这里的指针ptr被初始化为字符串“hello”，这是一个存储在只读存储器(ROM)中的常量字符串，所以“hello”不能被更改，因为它存储在ROM中

PTR存储在堆栈部分并指向常量字符串"hello"

所以ptr[0]='m'是无效的，因为你不能访问只读内存

但是ptr可以直接初始化为其他字符串值，因为它只是一个指针，所以它可以指向其数据类型变量的任何内存地址

ptr="new string"; is valid

在第一个代码中，"string"是一个字符串常量，字符串常量永远不应该被修改，因为它们通常被放置在只读内存中。"str"是一个用来修改常量的指针。

在第二段代码中，"string"是一个数组初始化器，类似于

char str[7] =  { 's', 't', 'r', 'i', 'n', 'g', '\0' };

"str"是堆栈上分配的数组，可以自由修改。

5.5节K&R的字符指针和功能也讨论了这个主题:

There is an important difference between these definitions: char amessage[] = "now is the time"; /* an array */ char *pmessage = "now is the time"; /* a pointer */ amessage is an array, just big enough to hold the sequence of characters and '\0' that initializes it. Individual characters within the array may be changed but amessage will always refer to the same storage. On the other hand, pmessage is a pointer, initialized to point to a string constant; the pointer may subsequently be modified to point elsewhere, but the result is undefined if you try to modify the string contents.