理解函数指针用C [英] Understanding functions and pointers in C

问题描述

这是一个很简单的问题，但到底是什么下面的函数原型是什么意思？

This is a very simple question but what does the following function prototype mean?

INT广场（INT Y，为size_t * X）

int square( int y, size_t* x )

什么贮藏为size_t *是什么意思？我知道为size_t是一种数据类型（INT> = 0）。但我怎么看*连接到它？它是一个指向x的内存位置？总的来说，我有这个东西的麻烦，如果有人可以提供一个方便的参考，我AP preciate它。

what dose the size_t* mean? I know size_t is a data type (int >=0). But how do I read the * attached to it? Is it a pointer to the memory location for x? In general I'm having trouble with this stuff, and if anybody could provide a handy reference, I'd appreciate it.

谢谢大家。我明白了一个指针是什么，但我想我有一个很难很难理解指针和功能之间的关系。当我看到定义为函数原型int平方米（INT X，int y）对，那么它是完全清楚，我是怎么回事。然而，当我看到类似 INT平方米（INT X，INT * Y），那么我不能 - 我的生活 - 明白的第二个参数的真正含义。在一定程度上我理解的意思是传递指针，但我不明白的东西不够好，操纵它在我自己的。

Thanks everybody. I understand what a pointer is, but I guess I have a hard hard time understanding the relationship between pointers and functions. When I see a function prototype defined as int sq(int x, int y), then it is perfectly clear to me what is going on. However, when I see something like int sq( int x, int* y), then I cannot--for the life of me--understand what the second parameter really means. On some level I understand it means "passing a pointer" but I don't understand things well enough to manipulate it on my own.

推荐答案

如何在理解教程指针？

在然而这种情况下，指针是可能用于修改/返回值。在C语言中，也有一个功能可以返回一个值（请原谅哑例子）两个基本机制：

In this case however, the pointer is probably used to modify/return the value. In C, there are two basic mechanisms in which a function can return a value (please forgive the dumb example):

它可以直接返回值：

float square_root( float x )
{
    if ( x >= 0 )
        return sqrt( x );
    return 0;
}

或者，它可以通过返回一个指针：

Or it can return by a pointer:

int square_root( float x, float* result )
{
    if ( x >= 0 )
    {
        *result = sqrt( result );
        return 1;
    }
    return 0;
}

第一个被称为：

float a = square_root( 12.0 );

...而后者

float b;
square_root( 12.00, &b );

请注意，后者的例子还可以让你检查值是否返回是真实的 - 这种机制被广泛应用于C库，其中一个函数的返回值通常表示成功（或缺乏），而值本身是通过参数返回。

Note that the latter example will also allow you to check whether the value returned was real -- this mechanism is widely used in C libraries, where the return value of a function usually denotes success (or the lack of it) while the values themselves are returned via parameters.

因此​​，与后者你可以写：

Hence with the latter you could write:

float sqresult;
if ( !square_root( myvar, &sqresult ) )
{
   // signal error
}  
else
{ 
   // value is good, continue using sqresult!
}

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