C++ 将 cout 输出输出到 std::string

getting cout output to a std::string

提问by venkysmarty

I have the following coutstatement. I use char arrays because I have to pass to vsnprintfto convert variable argument list and store in Msg.

我有以下cout声明。我使用 char 数组，因为我必须传递到vsnprintf以转换变量参数列表并存储在Msg.

Is there any way we can get coutoutput to C++ std::string?

有什么办法可以将cout输出输出到 C++std::string吗？

char Msg[100];
char appname1[100];
char appname2[100];
char appname3[100]; 

// I have some logic in function which some string is assigned to Msg.
std::cout << Msg << " "<< appname1 <<":"<< appname2 << ":" << appname3 << " " << "!" << getpid() <<" " << "~" << pthread_self() << endl;

回答by Bj?rn Pollex

You can replace coutby a stringstream.

您可以替换cout为stringstream.

std::stringstream buffer;
buffer << "Text" << std::endl;

You can access the string using buffer.str().

您可以使用buffer.str().

To use stringstreamyou need to use the following libraries:

要使用，stringstream您需要使用以下库：

#include <string>  
#include <iostream> 
#include <sstream>   

回答by graphite

You can use std::stringstream

您可以使用 std::stringstream

http://www.cplusplus.com/reference/iostream/stringstream/

http://www.cplusplus.com/reference/iostream/stringstream/

回答by CashCow

If you can change the code then use ostringstream (or stringstream) instead of cout.

如果您可以更改代码，请使用 ostringstream（或 stringstream）而不是 cout。

If you cannot change the code and want to "capture" what is being output you can redirect your output or pipe it.

如果您无法更改代码并想要“捕获”正在输出的内容，您可以重定向您的输出或通过管道传输它。

It may then be possible for your process to read the file or get the piped information through shared memory.

然后，您的进程就有可能通过共享内存读取文件或获取管道信息。

回答by John D Aynedjian

#include <stdio.h>

#include <iostream>
#include <string>
#include <sstream>

// This way we won't have to say std::ostringstream or std::cout or std::string...
using namespace std;

/** Simulates system specific method getpid()... */
int faux_getpid(){
    return 1234;
}

/** Simulates system specific method pthread_self()... */
int faux_pthread_self(){
    return 1111;
}

int main(int argc, char** argv){

    // Create a char[] array of 100 characters...
    // this is the old-fashioned "C" way of storing a "string"
    // of characters..
    char Msg[100];


    // Try using C++-style std::string rather than char[],
    // which can be overrun, leading to 
    // a segmentation fault.
    string s_appname1; 

    // Create old-fashioned char[] array of 100 characters...
    char appname2[100];

    // Create old-fashioned char[] array of 100 characters...
    char appname3[100]; 

    // Old-fashioned "C" way of copying "Hello" into Msg[] char buffer...
    strcpy(Msg, "Hello");

    // C++ way of setting std::string s_appname equal to "Moe"...
    s_appname1 = "Moe";

    // Old-fashioned "C" way of copying "Larry" into appname2[] char buffer...
    strcpy(appname2, "Larry");

    // Old-fashioned "C" way of copying "Shemp" into appname3[] char buffer...
    strcpy(appname3, "Shemp");

    // Declare le_msg to be a std::ostringstream...
    // this allows you to use the C++ "put-to" operator <<
    // but it will "put-to" the string-stream rather than
    // to the terminal or to a file...
    ostringstream le_msg;

    // Use put-to operator << to "write" Msg, s_appname1, s_appname2, etc...
    // to the ostringstream...not to the terminal...
    le_msg << Msg << " "<< s_appname1 <<":"<< appname2 << ":" << appname3 << " " << "!" << faux_getpid() <<" " << "~" << faux_pthread_self();

    // Print the contents of le_msg to the terminal -- std::cout --
    // using the put-to operator << and using le_msg.str(),
    // which returns a std::string.
    cout << "ONE: le_msg = \"" << le_msg.str() << "\"..." << endl;

    // Change contents of appname3 char[] buffer to "Curly"...
    strcpy(appname3, "Curly");

    // Clear the contents of std::ostringstream le_msg
    // -- by setting it equal to "" -- so you can re-use it.
    le_msg.str(""); 

    // Use put-to operator << to "write" Msg, s_appname1, s_appname2, etc...
    // to the newly cleared ostringstream...not to the terminal...
    // but this time appname3 has been set equal to "Curly"...
    le_msg << Msg << " "<< s_appname1 <<":"<< appname2 << ":" << appname3 << " " << "!" << faux_getpid() <<" " << "~" << faux_pthread_self();

    // Print the new contents of le_msg to the terminal using the  
    // put-to operator << and using le_msg.str(),
    // which returns a std::string.
    cout << "TWO: le_msg = \"" << le_msg.str() << "\"..." << endl;

    // This time, rather than using put-to operator << to "write"
    // to std::ostringstream le_msg, we'll explicitly set it equal
    // to "That's all Folks!"
    le_msg.str("That's all Folks!");

    // Print the new contents of le_msg "That's all Folks!" to  
    // the terminal via le_msg.str()
    cout << "THREE: le_msg = \"" << le_msg.str() << "\"..." << endl;

    // Exit main() with system exit value of zero (0), indicating
    // success...
    return 0;

}/* main() */

OUTPUT:

输出：

ONE: le_msg = "Hello Moe:Larry:Shemp !1234 ~1111"...
TWO: le_msg = "Hello Moe:Larry:Curly !1234 ~1111"...
THREE: le_msg = "That's all, folks!"...