查询std :: ostringstream内容 [英] Query std::ostringstream content

问题描述

可以搜索 std :: ostringstream 的内容，而不使用 std :: ostringstream :: str（）成员函数创建一个 std :: string 来搜索？

Is it possible to search the content of a std::ostringstream without using the std::ostringstream::str() member function to create a std::string to search?

避免在每次调用 flush _（）时构造 std :: string 实例：

I have the following and want to avoid constructing a std::string instance on every invocation of flush_():

#include <iostream>
using std::cout;

#include <ios>
using std::boolalpha;

#include <sstream>
using std::ostringstream;

#include <string>
using std::string;

class line_decorating_ostream
{
public:
    line_decorating_ostream()  { out_ << boolalpha;  }
    ~line_decorating_ostream() { cout << out_.str(); }

    template <typename T>
    line_decorating_ostream& operator<<(const T& a_t)
    {
        out_ << a_t;
        flush_();
        return *this;
    }

private:
    ostringstream out_;
    line_decorating_ostream(const line_decorating_ostream&);
    line_decorating_ostream& operator=(const line_decorating_ostream&);

    // Write any full lines.
    void flush_()
    {
        string s(out_.str());
        size_t pos = s.find('\n');
        if (string::npos != pos)
        {
            do
            {
                cout << "line: [" << s.substr(0, pos) << "]\n";
                s = s.substr(pos + 1);

            } while (string::npos != (pos = s.find('\n')));

            out_.clear();
            out_.str("");
            out_ << boolalpha << s;
        }
    }
};

int main()
{
    line_decorating_ostream logger;

    logger << "1 " << "2 " << 3 << " 4 " << 5 << "\n"
           << "6 7 8 9 10\n...\n" << true << "\n";

    return 0;
}

[它不会引起我担心的任何性能问题]

推荐答案

使用 streambuf 类？还是自己写一个？ （Ok：你应该自己写一个： pbase 和 pptr 都受到保护。）

Use its streambuf class? Or write an own one? (Ok: you should write an own one: pbase and pptr are protected.)

class my_str_buffer : public basic_stringbuf<char>
{
  public:
    using basic_stringbuf<char>::pbase;
    using basic_stringbuf<char>::pptr;
};

my_str_buffer my_buf;
ostream str( &my_buf );
// do anything
string foo( str.rdbuf()->pbase(), str.rdbuf()->pptr() );

ostream 构造函数和 stringbuf

ostream constructor and stringbuf

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