c - 指针及其取消引用的方法

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我对取消引用指针有疑问我编写了一个简单的代码，但我不知道它在某些情况下失败的原因，有人可以告诉它失败的原因是什么。如果我们有 char *ptr = "stack overflow"那么编译器自己会为其分配内存。

int main()
{
   int *ptr = 10;
   double *dptr = 111.111
   printf("%d", *ptr); //will give segmentation violation as we are trying to access the content in location 10
   printf("%d", ptr);//o/p will be 10 
   printf("%lf", dptr); // will give segmentation violation 
   printf("%lf", *dptr); // will give segmentation violation

}

Answer 1

int *ptr = 10;
double *dptr = 111.111

问题出在上面两行。

ptr指向地址10，而dptr我不知道它指向哪里。

取消引用这些指针肯定会产生未定义的行为..通常是分段违规错误。

修复:

int main(){
   int iVal = 10; 
   double dVal = 111.11;

   int *ptr = &iVal;
   double *dptr = &dval;

   printf("%d", *ptr); // ok
   printf("%p", (void *)ptr);// ok
   printf("%p", (void *)dptr); // ok
   printf("%lf", *dptr); // ok
   return 0;
}

<小时/>

理论:指针是一个保存地址的变量 - 或者正如 Alexey Frunze 所说:

The C standard does not define what a pointer is internally and how it works internally. This is intentional so as not to limit the number of platforms, where C can be implemented as a compiled or interpreted language.

A pointer value can be some kind of ID or handle or a combination of several IDs (say hello to x86 segments and offsets) and not necessarily a real memory address. This ID could be anything, even a fixed-size text string. Non-address representations may be especially useful for a C interpreter.