将 cout 输出输出到 std::string

Question

我有以下 cout 语句。我使用 char 数组，因为我必须传递给 vsnprintf 来转换变量参数列表并存储在 Msg 中。

有什么方法可以将 cout 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;

Answer 1

您可以将 cout 替换为 stringstream 。

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

您可以使用 buffer.str() 访问该字符串。

要使用stringstream，您需要使用以下库：

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

Answer 2

您可以使用 std::stringstream

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

Answer 3

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

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

然后，您的进程就可以读取文件或通过共享内存获取管道信息。

Answer 4

#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() */

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!"...