如何比较数组的内容相等性

发布于 2024-12-02 06:58:50 字数 242 浏览 1 评论 0原文

有没有办法让相等运算符用于比较相同类型的数组？

例如：

int x[4] = {1,2,3,4};
int y[4] = {1,2,3,4};
int z[4] = {1,2,3,5};
if (x == y) cout << "It worked!"

我知道它只是比较指针值 - 但我希望有某种 typedef 技巧或类似的东西，这样它就不需要循环或 memcmp 调用。

原文

Is there a way to get the equality operators to work for comparing arrays of the same type?

For example:

int x[4] = {1,2,3,4};
int y[4] = {1,2,3,4};
int z[4] = {1,2,3,5};
if (x == y) cout << "It worked!"

I'm aware that as is, it's just comparing pointer values - but I was hoping there's some kind of typedef trick or something like that so it wouldn't need a loop or a memcmp call.

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不回头走下去 2024-12-09 06:58:50

您可以使用标准 std::equal算法（或 std::ranges::equal 自 C++20 起）：

if (std::equal(x, std::end(x), y)) cout << "It worked!";
// or since C++20
if (std::ranges::equal(x, y)) cout << "It worked!";

You can use the standard std::equal algorithm (or std::ranges::equal since C++20):

if (std::equal(x, std::end(x), y)) cout << "It worked!";
// or since C++20
if (std::ranges::equal(x, y)) cout << "It worked!";

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又爬满兰若 2024-12-09 06:58:50

使用 std::equal 作为：

if(std::equal(x, x+ xsize, y)) std::cout << "equal";

它检查相同顺序的元素是否相等。这意味着，根据 std::equal 以下数组不相等。

int x[4] = {1,2,3,4};
int y[4] = {1,2,4,3}; //order changed!

Use std::equal as:

if(std::equal(x, x+ xsize, y)) std::cout << "equal";

It checks equality of elements in the same order. That means, according to std::equal the following arrays are not equal.

int x[4] = {1,2,3,4};
int y[4] = {1,2,4,3}; //order changed!

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你是暖光i 2024-12-09 06:58:50

另一种方法是将数组包装在 std::array 模板中，这将为数组创建一个小型包装类。一切都与正常情况非常相似，只是您获得了 operator= 的默认定义，因此您可以正常使用 == 来完成预期的操作。

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橙味迷妹 2024-12-09 06:58:50

由于数组具有相同的类型和长度，因此您可以使用 memcmp 来测试相等性，即值和位置相等：

int array1[4] = {1, 2, 3, 4};
int array2[4] = {5, 6, 7, 8};

if (memcmp(array1, array2, sizeof(array1)) == 0)
{
    cout << "arrays are equal" << "\n";
}
else
{
    cout << "arrays are not equal" << "\n";
}

Since the arrays are of the same type and length, you could use memcmp to test for equality, that is equality of value and position:

int array1[4] = {1, 2, 3, 4};
int array2[4] = {5, 6, 7, 8};

if (memcmp(array1, array2, sizeof(array1)) == 0)
{
    cout << "arrays are equal" << "\n";
}
else
{
    cout << "arrays are not equal" << "\n";
}

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探春 2024-12-09 06:58:50

解决方案 A - 使用 `std::array`^(C++11)

std::array<int> x = {1, 2, 3, 4};
std::array<int> y = {1, 2, 3, 4};
if (x == y) // true

std::array 一般可以避免很多 C 风格的数组问题，因此您可能需要用它替换所有对 int[] 的使用。

解决方案 B - 使用 `std::span`s^(C++20)

if (std::span{x} == std::span{y})

std::span 是数组的轻量级非拥有视图。
将范围包装在 std::span 中并使用 == 运算符应该与使用标准库算法一样便宜。

解决方案 C - 使用 `std::equal`^(C++98) 或 `std::ranges::equal`^{(C++ 20)}

if (std::ranges::equal(x, y))

// the last argument is optional, but may be helpful for optimizations
if (std::equal(std::begin(x), std::end(x), std::begin(y), std::end(y))

Solution A - Use `std::array`^(C++11)

std::array<int> x = {1, 2, 3, 4};
std::array<int> y = {1, 2, 3, 4};
if (x == y) // true

std::array avoids a lot of C-style array problems in general, so you might want to replace all your uses of int[] with it.

Solution B - Use `std::span`s^(C++20)

if (std::span{x} == std::span{y})

std::span is a lightweight non-owning view into an array.
Wrapping a range in a std::span and using the == operator should be just as cheap as using standard library algorithms.

Solution C - Use `std::equal`^(C++98) or `std::ranges::equal`^(C++20)

if (std::ranges::equal(x, y))

// the last argument is optional, but may be helpful for optimizations
if (std::equal(std::begin(x), std::end(x), std::begin(y), std::end(y))

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