Question

阅读无效指针： -

当我们将整数地址分配给void指针时，指针将变为Integer Pointer。
当我们将字符数据类型的地址分配给void指针时，它将变为Character Pointer。

代码：

  void main()
  {
  float f = 111.35;
  void * fp;
  fp = &f;
  printf("%.2f\n",*fp);
  }

它显示以下错误：void指针的使用无效如果我将指针的类型更改为float * fp，则没有错误。

Answer 1

void指针的类型是＆＃34;指向void＆＃34的指针;没有别的。由于void没有类型，因此在解除引用时必须将其显式转换为正确的类型，例如

*(float *) fp;

Answer 2

您的变量类型必须在printf之前或printf中指定，因此在将其转换为正确类型的c之前，您无法访问void *变量。

Answer 3

The prime benefit of using void pointer is its reusability.
You can use fp to point to a char* or int* or float* in successive statements.
When you state vp =&f, it implies that vp can act as a float pointer.
It does not become a float pointer.
So when you dereference it ( as in printf), you need to typecast it.

int main()
{
int iVal = 9;
float fVal = 9.0;
void *ptr;

ptr = &iVal; 
printf("iVal = %d\n",*((int*)ptr)); //De-referencing

//Resuability
ptr = &fVal;  
printf("fVal = %f\n",*((float*)ptr)); //De-referencing

return(0);
}

错误：无效指针的使用无效

3 个答案: