为什么不std :: getline阻止？ [英] Why doesn't std::getline block?

问题描述

我在Objective-C类中有一个代码（在Objective-C ++文件中）：

I have this code in an Objective-C class (in an Objective-C++ file):

+(NSString *)readString
{
    string res;
    std::getline(cin, res);
    return [NSString stringWithCString:res.c_str() encoding:NSASCIIStringEncoding];
}

当我运行它，我得到一个零长度的字符串，每次。从来没有给出在命令行输入的机会。没有。当我将此代码逐字复制到 main（），它工作。我在构建设置下有ARC。我不知道它是怎么回事。 OSX 10.7.4，Xcode 4.3.2。

When I run it, I get a zero-length string, Every time. Never given the chance to type at the command line. Nothing. When I copy this code verbatim into main(), it works. I have ARC on under Build Settings. I have no clue what it going on. OSX 10.7.4, Xcode 4.3.2.

推荐答案

这意味着有输入等待在输入上读取。您可以清空输入：

It means there is input waiting to be read on the input. You can empty the input:

cin.ignore(std::numeric_limits<std::streamsize>::max();
std::getline(cin, res);

上面的代码将在尝试读取更多内容之前删除任何用户输入。

If this is happening it means you did not read all the data off the input stream in a previous read. The above code will trash any user input before trying to read more.

这可能意味着你是混合 operator>> 与 std :: getline（）用于读取用户输入。在你的应用程序中使用（std :: getline（））（你可以混合它们，你只需要更小心，删除'\\\
'后使用operator >>确保任何后续std :: getline（）不会混淆。

This probably means that you are mixing operator>> with std::getline() for reading user input. You should probably pick one technique and use that (std::getline()) throughout your application ( you can mix them you just have to be more careful and remove the '\n' after using operator>> to make sure any subsequent std::getline() is not confused..

如果您想读取一个数字，请读取该行，然后解析该行的数字：

If you want to read a number read the line then parse the number out of the line:

std::getline(cin, line);
std::stringstream  linestream(line);

linestream >> value;

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