我的For循环有什么问题？我得到警告：有符号和无符号整数表达式之间的比较[-Wsign-compare] [英] What is wrong with my For loops? i get warnings: comparison between signed and unsigned integer expressions [-Wsign-compare]

问题描述

#include <iostream>
#include <string>
#include <vector>
#include <sstream>


using namespace std;

int main() {

    vector<double> vector_double;
    vector<string> vector_string;
    ...


    while (cin >> sample_string)
        {
            ...
        }

    for(int i = 0; i <= vector_string.size(); i++)
        {
            ....
        }

    for (int i = 0; i < vector_double.size(); i++)
        ....


    return 0;
}

推荐答案

为什么 -Wsign-compare ？会出现警告

警告名称及其文本，暗示，问题是您正在比较有符号和无符号整数。通常假设这是一个意外。

As the name of the warning, and its text, imply, the issue is that you are comparing a signed and an unsigned integer. It is generally assumed that this is an accident.

为了避免这个警告，你只需要确保< （或任何其他比较运算符）既有签名，又有无符号。

In order to avoid this warning, you simply need to ensure that both operands of < (or any other comparison operator) are either both signed or both unsigned.

/ p>

How could I do better ?

编写用于循环的惯用方法是初始化 both 第一个语句中的计数器和限制：

The idiomatic way of writing a for loop is to initialize both the counter and the limit in the first statement:

for (std::size_t i = 0, max = vec.size(); i != max; ++i)

你也可以（也许应该）使用迭代器，而不是索引：

You could also (and probably should) use iterators instead of indices:

for (std::vector<int>::iterator it = vec.begin(), end = vec.end(); it != end; ++it)

迭代器适用于任何类型的容器，而下标限制为C -arrays， deque 和向量。

Iterators work for any kind of containers, while indices limit you to C-arrays, deque and vector.

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