‘`char * str =“asdf”和` `char str[] =“asdf”的差异，strtok不工作

Question

我的代码显示了这个问题。

   char str[] = "asdf=1=2=3"; // this works
   printf("type:  %s\n", typename(str)); // prints 'pointer to char'
   char *token = strtok(str, "=");
   printf("%s\n", token);

这不管用，为什么？

   char *str2 = "asdf=1=2=3"; // this wont work
   printf("type:  %s\n", typename(str2)); // prints 'pointer to char'
   printf("%s\n", str2);
   char *token2 = strtok(str2, "="); // segmentation fault
   printf("%s", token2); 

编辑:这是typename宏

#define typename(x) _Generic((x),        /* Get the name of a type */             \
                                                                                  \
        _Bool: "_Bool",                  unsigned char: "unsigned char",          \
         char: "char",                     signed char: "signed char",            \
    short int: "short int",         unsigned short int: "unsigned short int",     \
          int: "int",                     unsigned int: "unsigned int",           \
     long int: "long int",           unsigned long int: "unsigned long int",      \
long long int: "long long int", unsigned long long int: "unsigned long long int", \
        float: "float",                         double: "double",                 \
  long double: "long double",                   char *: "pointer to char",        \
       void *: "pointer to void",                int *: "pointer to int",         \
      default: "other")

Answer 1

原因如下

   char * pointer_to_readonly_memory_string = "asdf";
   char pointer_to_memory_on_the_stack[] = "asdf";

   // pointer_to_readonly_memory_string[0] = 'b'; // segmentation fault
   pointer_to_memory_on_the_stack[0] = 'b';

   printf(" pointer_to_readonly_memory_string: %s\n", pointer_to_readonly_memory_string);
   printf(" pointer_to_memory_on_the_stack: %s\n", pointer_to_memory_on_the_stack);

char * varname = "asdf";

当您使用asteriks *初始化字符串并使用=赋值时，双引号"asdf"中的字符串将把字符串文字"asdf"放置在内存的只读部分，并使varname成为指向该值的指针，这使得对此内存的任何写入操作都是非法的。

char * varname = "asdf";

当您使用方括号[]并使用=赋值时，它将文本字符串放入只读内存中，再加上它将字符串复制到堆栈上新分配的内存中。这意味着内存是可以修改的。所以你可以这么做：varname[0] = 'b';