在 C++ 中连接字符串流
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原文地址: http://stackoverflow.com/questions/8231746/
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concatenate stringstream in c++
提问by Carlitos Overflow
How can I concatenate two stringstreams?
如何连接两个字符串流？
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include "types.h"
int main () {
char dest[1020] = "you";
char source[7] = "baby";
stringstream a,b;
a << source;
b << dest;
a << b; /*HERE NEED CONCATENATE*/
cout << a << endl;
cout << a.str() << endl;
return 0;
}
The output is the following in both tries:
两次尝试的输出如下：
0xbf8cfd20
baby0xbf8cfddc
The desired output is babyyou.
所需的输出是babyyou。
回答by jli
Should be:
应该：
b << dest;
a << b.str();
stringstream::strreturns the underlying string in the stringstream.
stringstream::str返回stringstream.
回答by Michael Krelin - hacker
Or
或者
a << b.rdbuf();
provided that get pointer is on the beginning of the stream to avoid allocating yet another std::stringfor content.
前提是 get 指针位于流的开头以避免std::string为内容分配另一个指针。
回答by Nawaz
You don't need two instance of std::stringstream. One is enough for the purpose.
你不需要两个std::stringstream. 一个就够了。
std::stringstream a;
a << source << dest;
std::string s = a.str(); //get the underlying string
回答by sehe
More generically across iostreams:
更一般地跨 iostream：
std::istream is1, is2; // eg. (i)stringstream
std::ostream os; // eg. (o)stringstream
os << is1.rdbuf();
os << is2.rdbuf();
os << std::flush;
This works for filestreams, std::cin etc. as well as for stringstream
这适用于文件流、std::cin 等以及字符串流
回答by FailedDev
Just replace a << bwith a << b.str()
只需替换 a << b为a << b.str()
回答by Mr Ed
The question was "how to concatenate STREAMS", the answers explained how to concatenate the contents of the streams. Here is a class which can be used to concatenate two istreams into one istream (file ConcatStreams.h):
问题是“如何连接流”，答案解释了如何连接流的内容。这是一个可用于将两个 istream 连接成一个 istream（文件 ConcatStreams.h）的类：
class ConcatStreams
: public std::streambuf {
std::streambuf* sbuf1_;
std::streambuf* sbuf2_;
char* buffer_;
int useBuf;
int bufSize;
public:
ConcatStreams(std::streambuf* sbuf1, std::streambuf* sbuf2)
: bufSize(1024), sbuf1_(sbuf1), sbuf2_(sbuf2), buffer_(new char[bufSize]), useBuf(1) {
}
ConcatStreams(const ConcatStreams& orig);
virtual ~ConcatStreams() { delete[] this->buffer_; }
int underflow() {
if (this->gptr() == this->egptr()) {
// get data into buffer_, obtaining its input from
// this->sbuf_; if necessary resize buffer
// if no more characters are available, size == 0.
std::streamsize size=0;
if(useBuf==1) {
size = this->sbuf1_->sgetn(this->buffer_, bufSize);
if(!size) { useBuf++;}
}
if(useBuf==2) {
size = this->sbuf2_->sgetn(this->buffer_, bufSize);
if(!size) { useBuf++;}
}
this->setg(this->buffer_, this->buffer_, this->buffer_ + size);
}
return this->gptr() == this->egptr()
? std::char_traits<char>::eof()
: std::char_traits<char>::to_int_type(*this->gptr());
}
};
To use it:
要使用它：
#include "ConcatStreams.h"
istringstream msgIn1("this is a stream.");
istringstream msgIn2("this is another stream.");
ConcatStreams cs(msgIn1.rdbuf(), msgIn2.rdbuf());
istream msgIn(&cs);
cout << "'" << msgIn.rdbuf() << "'" << endl;
Basically the class uses the streambuf's from the streams passed to it to create a new streambuf which first reads the first streambuf and then reads the second streambuf when finished with the first one.
基本上，该类使用传递给它的流中的流缓冲来创建一个新的流缓冲，该流缓冲首先读取第一个流缓冲，然后在完成第一个流缓冲后读取第二个流缓冲。
