standard-library

问题 This question already has answers here : What is going on with 'gets(stdin)' on the site coderbyte? (3 answers) Closed 4 months ago . I am new to C programming (although I have experience with Java). After reading some tutorials, I decided to start solving coding challenges on Coderbyte. The first challenge I tried was this one: Challenge Have the function FirstFactorial(num) take the num parameter being passed and return the factorial of it. For example: if num = 4, then your program should

问题 I found this line in stdio.h : extern struct _IO_FILE *stdin; Based on this 'extern' keyword, i assume this is just a declaration. I wonder where is stdin defined and initialized? 回答1: It's defined in the source code of your C library. You typically only need the headers for compilation, but you can find the source code for many open-source standard libraries (like glibc). In glibc, it's defined in libio/stdio.c as like this: _IO_FILE *stdin = (FILE *) &_IO_2_1_stdin_; Which is in turn

问题 Closed. This question is off-topic. It is not currently accepting answers. Want to improve this question? Update the question so it's on-topic for Stack Overflow. Closed 5 years ago . There is a study group in the C++ standardization committee to provide compile-time reflection in C++1z or after. I would like to know what is exactly the purpose and how powerful the expected tools will be? For example will it be possible to name functions or classes using these tools? struct A {int f() {return

问题 Consider a function of the following general form: Foo findFoo(Collection<Foo> foos, otherarguments) throws ObjectNotFoundException { for(Foo foo : foos){ if(/* foo meets some condition*/){ return foo; } } throw new ObjectNotFoundException(); } A concrete case, for example, would be: User findUserByName(Collection<User> users, String name) throws ObjectNotFoundException { for(User user : users){ if(user.getName().equals(name)){ return user; } } throw new ObjectNotFoundException(); } These

问题 Those of us who have seen the beauty of STL try to use it as much as possible, and also encourage others to use it wherever we see them using raw pointers and arrays . Scott Meyers have written a whole book on STL, with title Effective STL. Yet what happened to the developers of ifstream that they preferred char* over std::string . I wonder why the first parameter of ifstream::open() is of type const char* , instead of const std::string & . Please have a look at it's signature: void open

问题 I'm using an istream which could be stringstream, ifstream or a user-defined stream type and I need to know if, in the case of an ifstream, it was not opened in binary mode (so I can throw an exception). I have tried the following method: if ((_is.flags() & ios::binary) == 0) throw exception(...) but no exception is ever thrown. The test fails in this case because _is.flags() returns 0x201 and ios::binary is 0x20. Is there a way to find out if a stream was opened in text mode? 回答1: flags()

问题 I came across this - in my view - strange behaviour: "a b c".split(maxsplit=1) TypeError: split() takes no keyword arguments Why does str.split() not take keyword arguments, even though it would make sense? I found this behavior both in Python2 and Python3. 回答1: See this bug and its superseder. str.split() is a native function in CPython, and as such exhibits the behavior described here: CPython implementation detail: An implementation may provide built-in functions whose positional

问题 What are the reasons for the existence of std::decay? In what situations is std::decay useful? 回答1: <joke>It's obviously used to decay radioactive std::atomic types into non-radioactive ones.</joke> N2609 is the paper that proposed std::decay . The paper explains: Simply put, decay<T>::type is the identity type-transformation except if T is an array type or a reference to a function type. In those cases the decay<T>::type yields a pointer or a pointer to a function, respectively. The

问题 Given this C++11 program, should I expect to see a number or a letter? Or not make expectations? #include <cstdint> #include <iostream> int main() { int8_t i = 65; std::cout << i; } Does the standard specify whether this type can or will be a character type? 回答1: From § 18.4.1 [cstdint.syn] of the C++0x FDIS (N3290), int8_t is an optional typedef that is specified as follows: namespace std { typedef signed integer type int8_t; // optional //... } // namespace std § 3.9.1 [basic.fundamental]

问题 I know most compilers allow both: #include <stdio.h> //and #include <cstdio> But someone argued that <stdio.h> is not actually C++ standard. is that true? 回答1: stdio.h is standard, but deprecated. Always prefer cstdio in C++. [n3290: C.3.1/1]: For compatibility with the Standard C library, the C++ standard library provides the 18 C headers (D.5), but their use is deprecated in C++. [n3290: D.5/3]: [ Example: The header <cstdlib> assuredly provides its declarations and definitions within the