stdstring

问题 I'm trying to create a function that takes a variable amount of std::string arguments and formats a string with it. Example: Test::formatLine(const string::format, ...) { const std::string buffer; va_list args; va_start(args, format); vsprintf(buffer.c_str, format.c_str, args); va_end(args); cout << buffer << endl; } Compiling this snippet errors: Error 1 error C3867: 'std::basic_string<char,std::char_traits<char>,std::allocator<char>>::c_str': function call missing argument list; use '&std:

问题 Justin's answer on another question made an observation that I find very interesting but can't quite explain. Consider the following code: std::vector<std::string> v; v.push_back("Hello, world!"); // Doesn't call strlen. v.emplace_back("Hello, world!"); // Calls strlen. If you look at the assembly, emplace_back generates a call to strlen, whereas push_back does not (tested in gcc 8.1 and clang 6.0 using -Ofast ). Why is this happening? Why can't emplace_back optimize out the strlen call here?

问题 So C++ 14 introduced a number of user-defined literals to use, one of which is the "s" literal suffix, for creating std::string objects. According to the documentation, its behavior is exactly the same as constructing an std::string object, like so: auto str = "Hello World!"s; // RHS is equivalent to: std::string{ "Hello World!" } Of course constructing an unnamed std::string object could be done prior to C++ 14, but because the C++ 14 way is so much simpler, I think way more people will

问题 I have a string std::string s = "Stack Overflow"; That I need to copy into a vector. This is how I am doing it std::vector<char> v; v.reserve(s.length()+1); for(std::string::const_iterator it = s.begin(); it != s.end(); ++it) { v.push_back( *it ); } v.push_back( '\0' ); But I hear range operation are more efficient. So I am thinking something like this std::vector<char> v( s.begin(), s.end()); v.push_back('\0'); But is this better in this case? What about the potential re-allocation when

问题 I'm trying to use a std::string as a key in a std::map however, i'm unable to find() correctly. My code is somewhat complicated and large so this is a small program that demonstrates the problem I'm having. If someone could tell me why this doesn't work, i'd be very grateful. Thanks. #include <stdio.h> #include <string> #include <map> struct comparer { public: bool operator()(const std::string x, const std::string y) { return x.compare(y)==0; } }; int main(int argc, char *argv[]) { std::map

问题 I have a fairly simple log() method for a GL shader and program convenience classes, since the respective compile and link methods only return a bool , while hiding all the GL calls; e.g., std::string glShader::log () const { std::string info; GLint len = 0; if (!glIsShader(gl_shader_obj)) info = "(invalid shader object)\n"; else glGetShaderiv(gl_shader_obj, GL_INFO_LOG_LENGTH, & len); if (len != 0) { info.resize(static_cast<std::string::size_type>(len)); glGetShaderInfoLog(gl_shader_obj, len

问题 Is it possible to use an std::string for read() ? Example : std::string data; read(fd, data, 42); Normaly, we have to use char* but is it possible to directly use a std::string ? (I prefer don't create a char* for store the result) Thank's 回答1: Well, you'll need to create a char* somehow, since that's what the function requires. (BTW: you are talking about the Posix function read , aren't you, and not std::istream::read ?) The problem isn't the char* , it's what the char* points to (which I

问题 Why is it that you can insert a '\0' char in a std::basic_string and the .length() method is unaffected but if you call char_traits<char>::length(str.c_str()) you get the length of the string up until the first '\0' character? e.g. string str("abcdefgh"); cout << str.length(); // 8 str[4] = '\0'; cout << str.length(); // 8 cout << char_traits<char>::length(str.c_str()); // 4 回答1: Great question! The reason is that a C-style string is defined as a sequence of bytes that ends with a null byte.

问题 I'm writing some C++11 code that makes assumptions about the nature of std::string that are valid, but represent behavior that was changed in C++11. In the earlier days, libstdc++'s basic_string implementation conformed to the 98/03 requirements, but not to the more strict C++11 requirements. As I understand it, libstdc++ has fixed the issues around basic_string . The problem is that there are many versions of the library that people use which do not implement this fix. And my code may

问题 How to fix a Visual Studio 2012 error LNK2019: unresolved external symbol "__declspec(dllimport) public: class std::basic_string? I've been compiling a solution containing one exe and several static lib projects on which the exe depends fine with Visual Studio 2008. The static libs include: TCL: tcl84tsx.lib wxWidgets: wxbase.lib zlib.lib ws2_32.lib xerces-c_2.lib SNMP Research EMANATE: subagent.lib,agent.lib,emanate.lib,pack.lib,mibtable.lib,devkit.lib etc. I loaded the solution into Visual