如何可靠地获得C风格的数组的大小？ [英] How to reliably get size of C-style array?

问题描述

我如何可靠地得到一个C数组的大小？经常推荐的方法似乎是使用的sizeof ，但它并没有在富函数，其中正常工作 X 中传递：

How do I reliably get the size of a C-style array? The method often recommended seems to be to use sizeof, but it doesn't work in the foo function, where x is passed in:

#include <iostream>

void foo(int x[]) {
  std::cerr << (sizeof(x) / sizeof(int)); // 2  
}

int main(){
    int x[] = {1,2,3,4,5};
    std::cerr << (sizeof(x) / sizeof(int)); // 5                              
    foo(x);
    return 0;
}

解答<一个href=\"http://stackoverflow.com/questions/1969588/looping-a-fixed-size-array-without-defining-its-size-in-c\">this问题建议的sizeof ，但他们不说，它（显然？）不会，如果你通过围绕阵列工作。所以，我必须用一个哨兵呢？ （我不认为我的富功能的用户总是可以信任的把一个哨兵在最后。当然，我可以使用 STD ::矢量，但我没有得到漂亮的语法速记 {1,2,3,4,5} ）

Answers to this question recommend sizeof but they don't say that it (apparently?) doesn't work if you pass the array around. So, do I have to use a sentinel instead? (I don't think the users of my foo function can always be trusted to put a sentinel at the end. Of course, I could use std::vector, but then I don't get the nice shorthand syntax {1,2,3,4,5}.)

推荐答案

在C阵列参数C的真的只是这样的指针的sizeof（）将不起作用。你要么需要在大小传递作为另一个参数或使用定点 - 取其最适合您的设计

In C array parameters in C are really just pointers so sizeof() won't work. You either need to pass in the size as another parameter or use a sentinel - whichever is most appropriate for your design.

一些其他的选择：

其他的一些信息：

• 对于C ++，强似原始数组指针，你可能希望有参数使用的东西，包装在保持数组的大小轨道类模板阵列，并提供了方法，将数据复制到阵列以安全的方式。像 STLSoft的array_proxy模板或的Boost's提高::数组可能的帮助。我以前用过的 array_proxy 模板不错的效果。使用参数的函数内部，你会得到的std ::矢量一样操作，但该函数的调用者可以使用一个简单的C数组。有没有数组的复制 - 对 array_proxy 模板需要将近自动包装数组指针和数组的大小照顾

• for C++, instead of passing a raw array pointer, you might want to have the parameter use something that wraps the array in a class template that keeps track of the array size and provides methods to copy data into the array in a safe manner. Something like STLSoft's array_proxy template or Boost's boost::array might help. I've used an array_proxy template to nice effect before. Inside the function using the parameter, you get std::vector like operations, but the caller of the function can be using a simple C array. There's no copying of the array - the array_proxy template takes care of packaging the array pointer and the array's size nearly automatically.

宏在C用于确定元素的数量在数组（时的sizeof（）可能会帮助 - 也就是说，你不是一个简单的指针处理）：<一href=\"http://stackoverflow.com/questions/1598773/is-there-a-standard-function-in-c-that-would-return-the-length-of-an-array/1598827#1598827\">http://stackoverflow.com/questions/1598773/is-there-a-standard-function-in-c-that-would-return-the-length-of-an-array/1598827#1598827

a macro to use in C for determining the number of elements in an array (for when sizeof() might help - ie., you're not dealing with a simple pointer): http://stackoverflow.com/questions/1598773/is-there-a-standard-function-in-c-that-would-return-the-length-of-an-array/1598827#1598827

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