C ++读取文件令牌

问题描述

抱歉，另一个请求。.
现在我正在逐个读取令牌，它可以工作，但是我想知道何时有新行。.

another request sorry..Right now I am reading the tokens in one by one and it works, but I want to know when there is a new line..

如果我的文件包含

Hey Bob
Now

应该给我

Hey
Bob
[NEW LINE]
NOW

有没有办法

推荐答案

是的，运算符>>与字符串一起使用时，用'空白'分隔的单词。 空白包含空格标签和换行符。

Yes the operator>> when used with string read 'white space' separated words. A 'White space' includes space tab and new line characters.

如果您想一次读取一行，请使用std :: getline（）
$ b然后可以使用字符串流分别标记该行。

If you want to read a line at a time use std::getline()
The line can then be tokenized separately with a string stream.

std::string   line;
while(std::getline(std::cin,line))
{

    // If you then want to tokenize the line use a string stream:

    std::stringstream lineStream(line);
    std::string token;
    while(lineStream >> token)
    {
        std::cout << "Token(" << token << ")\n";
    }

    std::cout << "New Line Detected\n";
}

小添加：

因此，您真的希望能够检测到换行符。这意味着换行符成为另一种令牌。因此，假设您有用空白分隔的单词作为标记，而换行符作为其自己的标记。

So you really want to be able to detect a newline. This means that newline becomes another type of token. So lets assume that you have words separated by 'white spaces' as tokens and newline as its own token.

然后您可以创建标记类型。

然后，您所要做的就是为令牌编写流运算符：

Then you can create a Token type.
Then all you have to do is write the stream operators for a token:

#include <iostream>
#include <fstream>

class Token
{
    private:
        friend std::ostream& operator<<(std::ostream&,Token const&);
        friend std::istream& operator>>(std::istream&,Token&);
        std::string     value;
};
std::istream& operator>>(std::istream& str,Token& data)
{
    // Check to make sure the stream is OK.
    if (!str)
    {   return str;
    }

    char    x;
    // Drop leading space
    do
    {
        x = str.get();
    }
    while(str && isspace(x) && (x != '\n'));

    // If the stream is done. exit now.
    if (!str)
    {
        return str;
    }

    // We have skipped all white space up to the
    // start of the first token. We can now modify data.
    data.value  ="";

    // If the token is a '\n' We are finished.
    if (x == '\n')
    {   data.value  = "\n";
        return str;
    }

    // Otherwise read the next token in.
    str.unget();
    str >> data.value;

    return str;
}
std::ostream& operator<<(std::ostream& str,Token const& data)
{
    return str << data.value;
}


int main()
{
    std::ifstream   f("PLOP");
    Token   x;

    while(f >> x)
    {
        std::cout << "Token(" << x << ")\n";
    }
}

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