iostream

问题 I have just come accross Dan Stahlke's gnuplot C++ I/O interface, which saves me from "rolling my own". Unfortunately, there are not too may examples and there ios no real documentation. I have the following data types in my C++ project: struct Data { std::string datestr; // x axis value float f1; // y axis series 1 float f2; // y axis series 2 float f3; // y axis series 3 }; typedef std::vector<Data> Dataset; I want to pass a Dataset variable from C++, so that I can plot the data (dates on

问题 I'm a newbie to C++. Small code sample follows: int main(int argc, char* argv[]) { char ch1; int int1; cin >> ch1; cin >> int1; cout << ch1 << '\n'; cout << int1 << '\n'; return 0; } When I run the program and input the following: az I get as output: a 32767 I understand the 'a' but why the integer value of 32767? I just want to test and see what happen if instead of a numeric value assigned to int1 i used a 'z'. I try inputting: ax ...and I also get same results. Now if instead of int int1 I

问题 I'm trying to overload the ostream operator to allow output for a nested class inside a template. However, the compiler is unable to bind the actual function call to my overload. template <class T> struct foo { struct bar { }; }; template <class T> std::ostream& operator << (std::ostream& os, const typename foo<T>::bar& b) { return os; } int main() { foo<int>::bar b; std::cout << b << std::endl; // fails to compile } This will compile if I define the overload as an inline friend function:

问题 I'm trying to find a method to get the number of characters read or written to a stream that is reliable even if there is an error and the read/write ends short. I was doing something like this: return stream.rdbuf()->sputn(buffer, buffer_size); but if the streambuf implementation of overflow is permitted to throw excpections this won't work. Is it? I've not been able to find it documented anywhere. 回答1: basic_streambuf::overflow is allowed to throw an exception upon failure as documented in

问题 In one part of our application there is the requirement to format numbers according to the user's locale. The interface essentially looks like this: std::string format_number(double number); The old implementation looked like this: std::string format_number(double number) { using namespace std; static const locale user_loc(""); ostringstream fmtstream; fmtstream.imbue(user_loc); fmtstream << std::fixed; fmtstream << number; return fmtstream.str(); } We have now noticed that with our compiler

问题 I need at the end of main() execution to check if last char sent to stdout (through std::cout ) was '\n' (or platform specific end-of-line). How to test for this? It is safe to assume that C style io (like printf) was not used. Program is REPL for C++. It evaluates C++ expressions (or statements) and prints results on stdout. It is desirable that output would be always terminated with single new-line. 回答1: It is similar answer to this given by @Kevin. However I believe it is better for your

问题 I need at the end of main() execution to check if last char sent to stdout (through std::cout ) was '\n' (or platform specific end-of-line). How to test for this? It is safe to assume that C style io (like printf) was not used. Program is REPL for C++. It evaluates C++ expressions (or statements) and prints results on stdout. It is desirable that output would be always terminated with single new-line. 回答1: It is similar answer to this given by @Kevin. However I believe it is better for your

问题 My program prints a large number of short lines to cout . As a slightly contrived example, my lines look a little like this: cout<<"The variable's value is: "<<variable<<endl; I'd like the program to run fast and I do believe that endl is killing me because it initiates a buffer flush on cout every time it is used. Now, some folks on the internet have said that I could do this instead: cout<<"The variable's value is: "<<variable<<"\n"; But this does not seem like a good solution because endl

问题 Is there an available combination of std::ios::openmode to avoid modifications of an existing file and allow only the creation of a new one ? 回答1: No there isn't. See the C++03 Standard § 27.4.2.1.4/1, or the C++11 Standard § 27.5.3.1.4/1 if to hand or otherwise http://en.cppreference.com/w/cpp/io/ios_base/openmode. As none of the specified constants that may be |-conjoined to form an openmode implies that the opened file shall not exist no conjunction of them can have that implication. 来源：

问题 What are the possible options and the most appropiate for reading an executable file in Java. I want produce the hexadecimal representation of an .exe file. Im thinking of reading the file in binary and then doing the conversion. But how can i read the .exe? 回答1: 1) read the file in as bytes. use BufferedInputStream( new FileInputStream( new File("bin.exe") ) ) 2) convert each byte to hex format. static final String HEXES = "0123456789ABCDEF"; public static String getHex( byte [] raw ) { if (