iostream

A colleague just told me that this code: std::ifstream stream(filename.c_str()); if (!stream) { throw std::runtime_error(".."); } would be wrong. He said ifstream evaluates to 0 if opening is successful. My code works, but I wanted to find the documentation but didn't see where it says how to check if opening was successful. Can you point me to it? Oliver Charlesworth operator! is overloaded for std::ifstream , so you can do this. In my opinion, though, this is a horrible abuse of operator overloading (by the standards committee). It's much more explicit what you're checking if you just do if

I am using the GCC built-in type __int128 for a few things in my C++ program, nothing really significant, at least not enough to justify to use BigInt library only for that and, yet, enough to prevent to remove it totally. My problem comes when I run into the printing parts my classes, here is a minimal example: #include <iostream> int main() { __int128 t = 1234567890; std::cout << t << std::endl; return t; } Commenting out the std::cout line will make this code to compile nicely with g++ , but having it will cause the following error message: int128.c: In function ‘int main()’: int128.c:7:13:

以struct类型为例： 引用 #include"iostream" #include<string> using namespace std; struct mycoach { string name; int age; }; void printinfo1(mycoach &cpc) { //参数是mycoach实例的别名,指向入参的真实地址，所以一改入参的值也跟着改 cpc.name = "陈培昌"; } void main() { mycoach coach1; coach1.name = "徐晓冬"; printinfo1(coach1); cout << "这位神秘嘉宾是" << coach1.name << endl;//陈培昌 system("pause"); } 输出结果： 形参传入----可以预见这种方式不会改变struct实例的值 #include"iostream" #include<string> using namespace std; struct mycoach { string name; int age; }; void printinfo1(mycoach cpc) { //参数是mycoach实例的别名,指向入参的真实地址，所以一改入参的值也跟着改 cpc.name = "陈培昌"; } void main() { mycoach

What the difference between the following two loops and When each one will stopped ? #include<iostream> #include<algorithm> #include<vector> using namespace std; int main() { int x,y; while(cin >> x){ // code } while(cin){ cin >> y; //code } return 0; } Let's look at these independently: while(cin >> x) { // code } This loop, intuitively, means "keep reading values from cin into x , and as long as a value can be read, continue looping." As soon as a value is read that isn't an int , or as soon as cin is closed, the loop terminates. This means the loop will only execute while x is valid. On the

I'm trying to write a type trait to detect if a type has overloaded operator<<() suitable to use to an output stream. I'm missing something because I'm always getting true for a simple empty class with no operators at all. Here the code: template<typename S, typename T> class is_streamable { template<typename SS, typename TT> static auto test(SS&& s, TT&& t) -> decltype(std::forward<SS>(s) << std::forward<TT>(t)); struct dummy_t {}; static dummy_t test(...); using return_type = decltype(test(std::declval<S>(), std::declval<T>())); public: static const bool value = !std::is_same<return_type,

Experimenting with I/O I get an exception where no exception should have been thrown: #include <iostream> #include <fstream> int main() { std::ifstream f("/tmp"); std::cout << "Exception Flags: " << f.exceptions() << std::endl; if(f >> std::ws) std::cout << "This will not succeed" << std::endl; else std::cout << "Ok - it fails" << std::endl; return 0; } But the output is: Exception Flags: 0 terminate called after throwing an instance of 'std::ios_base::failure' what(): basic_filebuf::underflow error reading the file Aborted g++ (Ubuntu/Linaro 4.7.2-2ubuntu1) 4.7.2 Edit The test is supposed to

Abstract: I was expecting the code: cout << uint8_t(0); to print "0", but it doesn't print anything. Long version: When I try to stream uint8_t objects to cout, I get strange characters with gcc. Is this expected behavior? Could it be that uint8_t is an alias for some char-based type? See compiler/system notes in the code example. // compile and run with: // g++ test-uint8.cpp -std=c++11 && ./a.out // -std=c++0x (for older gcc versions) /** * prints out the following with compiler: * gcc (GCC) 4.7.2 20120921 (Red Hat 4.7.2-2) * on the system: * Linux 3.7.9-101.fc17.x86_64 * Note that the first