iostream

问题 According to http://en.cppreference.com/w/cpp/io/streamsize The type std::streamsize is a signed integral type used to represent the number of characters transferred in an I/O operation or the size of an I/O buffer. As far as I can imagine, a stream's size can never be negative, so, my question is: Why is std::streamsize defined as signed rather than unsigned ? What's the rationale behind? 回答1: The draft C++ standard has the following footnote 296 in section 27.5.2 Types which says:

来源： https://stackoverflow.com/questions/22624503/how-to-get-a-file-descriptor-from-a-stdbasic-ios-for-clang-on-os-x

来源： https://stackoverflow.com/questions/22624503/how-to-get-a-file-descriptor-from-a-stdbasic-ios-for-clang-on-os-x

来源： https://stackoverflow.com/questions/21389796/program-will-not-print-line-before-exit-function

来源： https://stackoverflow.com/questions/21631011/read-float-from-input-stream-without-trailing-e

问题 I want to print a double value to std::cout portably (GCC, clang, MSVC++) such that the output is the same on all platforms. I have a problem with the formatting of the exponent. The following program #include <iostream> int main() { std::cout << 0.1e-7 << std::endl; return 0; } Has this output with GCC: 1e-08 and the following output with MSVC 1e-008 How can I make both outputs the same? I'm sorry if this is a dumb question but I have not found an answer so far. All formatting seems to

问题 This error has only appeared for me since updating Xcode (and to MacOS Mojave 10.14). Something similar happened with #include <Python> , which I fixed by instead using #include "python2.7/Python.h". There is a similar error discussed in Clang doesn't see basic headers. When I try clang++ -stdlib=libc++ PyTrans.cpp -o -v I get ld: symbol(s) not found for architecture x86_64 clang: error: linker command failed with exit code 1 (use -v to see invocation) . The full error: warning: include path

问题 I am new to boost::iostreams so this might be trivial: Assuming namespace io = boost::iostreams; this works io::filtering_ostream out(std::cout); out << "some\nstring\n"; and this works std::string result; io::filtering_ostream out(io::counter() | io::back_inserter(result)); out << "some\nstring\n"; yet this does not compile io::filtering_ostream out(io::counter() | std::cout); out << "some\nstring\n"; How do you pipe into std::cout ? 回答1: Wrapping std::cout with boost::ref worked for me: io:

问题 I'm trying to learn C++ from an older edition of the Primer, and tried to execute some of their code relating to iostream objects, which gave me some trouble: #include <iostream> #include <cstdlib> using namespace std; int main(int argc, char *argv[]) { int ival; try { while (cin >> ival, !cin.eof()) { if (cin.bad()) throw runtime_error("IO stream corrupted"); if (cin.fail()) { cerr << "Invalid input - try again"; cin.clear(iostream::failbit); continue; } else cout << ival << endl; } return

问题 I'm trying to learn C++ from an older edition of the Primer, and tried to execute some of their code relating to iostream objects, which gave me some trouble: #include <iostream> #include <cstdlib> using namespace std; int main(int argc, char *argv[]) { int ival; try { while (cin >> ival, !cin.eof()) { if (cin.bad()) throw runtime_error("IO stream corrupted"); if (cin.fail()) { cerr << "Invalid input - try again"; cin.clear(iostream::failbit); continue; } else cout << ival << endl; } return