std :: getline和std :: vector< std :: string>的行为怪异 [英] Weird behaviour with std::getline and std::vector<std::string>

问题描述

我有以下代码:

std::vector<std::string> final_output;
std::string input;

int tries = 0;
std::cin >> tries;

int counter = 0;
while(counter < tries) {

    std::getline(std::cin, input); 
    final_output.push_back(input);
    ++counter;

}

输入:

3
Here Goes
Here Goes 2

输出为:

<blank line>
Here Goes
Here Goes 2

奇怪的是，它似乎是第一次运行时输入空白行.

Weirdly, it seems to enter a blank line as input for the first time it runs.

但是，如果我的代码为:

However, if I have the code as:

int tries = 3;         // explicitly specifying the number of tries
int counter = 0;
while(counter < tries) {}

它按预期工作.为什么 std :: cin>>尝试导致代码失败?

It works as expected. Why is the std::cin >> tries causing the code to fail?

我已经在VC ++ 2010和g ++ 4.4.3中对其进行了测试

I have tested it with VC++ 2010 and g++ 4.4.3

推荐答案

当您输入 tries 的数字时，您按了回车键.阅读 trys 后，按回车键返回的回车符仍位于输入缓冲区中.该回车符通常会转换为换行符.您对 getline 的下一次调用将读取输入缓冲区中的所有内容，直到下一行.由于第一个字符是换行符，因此将其读取为长度为零的行(即换行符之前为零个字符).

When you enter the number for tries, you hit the return key. After you read tries, the carriage return from hitting the return key is still sitting in the input buffer. That carriage return will normally be translated to a new-line character. Your next call to getline reads everything in the input buffer up to the next new-line. Since the first character is a new-line, it reads that as a line of zero length (i.e., zero characters before the new-line).

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