#include <iostream>
#include <fstream>
int main()
{
std::ofstream logFile("out.txt");
std::streambuf *outbuf = std::cout.rdbuf(logFile.rdbuf());
std::streambuf *errbuf = std::cerr.rdbuf(logFile.rdbuf());
// do the actual work of the program;
// GUI code and event loop would go here
std::cout << "This would normally go to cout but goes to the log file\n";
std::cerr << "This would normally go to cerr but goes to the log file \n";
logFile << "This goes to the log file\n";
// end of program body
// restore the buffers
std::cout.rdbuf(outbuf);
std::cerr.rdbuf(errbuf);
}
rdbuf函数返回一个由基类basic_ios管理的流缓冲区的指针。重载版本允许你替换流缓冲区，返回值是原始的流缓冲区。解决方法很简单—用你的log文件的流缓冲区替换cout和cerr的流缓冲区。程序结束时，改回原来的流缓冲区。