char *str = "string";

分配一个指向字符串字面量的指针，编译器将其放入可执行文件中不可修改的部分;

char str[] = "string";

分配并初始化一个可修改的本地数组

char *str = "string";  

上面的代码将str设置为指向在程序的二进制映像中硬编码的字面值“string”，它在内存中可能被标记为只读。

因此str[0]=试图写入应用程序的只读代码。我猜这可能依赖于编译器。

通常，当程序运行时，字符串字面值存储在只读内存中。这是为了防止您意外地更改字符串常量。在第一个例子中，"string"存储在只读内存中，*str指向第一个字符。当您试图将第一个字符更改为'z'时，会发生段错误。

在第二个例子中，字符串"string"被编译器从其只读母数组复制到str[]数组中。然后允许更改第一个字符。你可以通过打印每个地址来检查:

printf("%p", str);

同样，在第二个例子中打印str的大小会显示编译器已经为它分配了7个字节:

printf("%d", sizeof(str));

// 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. 

首先，str是一个指向"string"的指针。编译器允许将字符串字面量放在内存中不能写入，但只能读取的地方。(这真的应该触发一个警告，因为你将一个const char *分配给一个char *。你是禁用了警告，还是忽略了它们?)

第二，你在创建一个数组，它是你可以完全访问的内存，并用"string"初始化它。您正在创建一个字符[7](六个用于字母，一个用于结尾的'\0')，您可以对它做任何您喜欢的事情。

The C FAQ that @matli linked to mentions it, but no one else here has yet, so for clarification: if a string literal (double-quoted string in your source) is used anywhere other than to initialize a character array (ie: @Mark's second example, which works correctly), that string is stored by the compiler in a special static string table, which is akin to creating a global static variable (read-only, of course) that is essentially anonymous (has no variable "name"). The read-only part is the important part, and is why the @Mark's first code example segfaults.