try...catch.. 和预编译宏、assert

#include <iostream>#include <stdexcept>#include <cassert>using namespace std;int main(int argc, char* agrv[]){#ifndef NDEBUG cerr << "main start" << endl << "line: " << __LINE__<< endl;#endif char ch; while(cin >> ch) { assert( ch != 'x'); try { if (ch == 'y') throw runtime_error("Error: should not be y"); cout << "You input correct! you input is: " << ch << endl; } catch(runtime_error err) { cout << err.what() << endl << "try again?" << endl; char c; cin >> c; if( cin && c == 'n') break; } }}

编译时可以用：g++  -D NDEBUG   filename.cpp -o filename 来指定宏开关。

特别注意assert，它仅仅在调试中起作用，在非debug下编译的程序将忽略assert语句。所以，千万不能试图用assert来控制你的程序逻辑。