manipulators

来源： https://stackoverflow.com/questions/40833897/why-stduppercase-doesnt-work-with-strings

问题 PSPS: (a Pre-scripted Post-script) It has just come to mind that a more prescient question would have included the notion of: Is this non-display of "0x"(showbase) for zero-value integers a standard behaviour, or is it just a quirk of my MinGW implementation? It all began on a pleasant Sunday morning... I want to dump some Handles in their hex representation, and in a consistant, formatted way. I want a leading 0x and a fixed width , but this is proving to be elusive using the expected stream

问题 I was trying out the noskipws manipulator in C++ and I wrote following code. #include <iostream> #include <sstream> #include <string> using namespace std; int main() { string first, middle, last; istringstream("G B Shaw") >> first >> middle >> last; cout << "Default behavior: First Name = " << first << ", Middle Name = " << middle << ", Last Name = " << last << '\n'; istringstream("G B Shaw") >> noskipws >> first >> middle >> last; cout << "noskipws behavior: First Name = " << first << ",

问题 I was trying out the noskipws manipulator in C++ and I wrote following code. #include <iostream> #include <sstream> #include <string> using namespace std; int main() { string first, middle, last; istringstream("G B Shaw") >> first >> middle >> last; cout << "Default behavior: First Name = " << first << ", Middle Name = " << middle << ", Last Name = " << last << '\n'; istringstream("G B Shaw") >> noskipws >> first >> middle >> last; cout << "noskipws behavior: First Name = " << first << ",

问题 In Stroustrup's C++ book, there is an example of a custom manipulator taking an argument (pls see the attached code). I am confused about how the struct is created. In particular, it looks like there are two int arguments for the constructor of "smanip", one for the function pointer "ff", one for "ii". I don't understand how the int argument is passed to create the structure by using: cout << setprecision(4) << angle; In addition, what is the order these functions get called, and how the the

问题 I want to define a class MyStream so that: MyStream myStream; myStream << 1 << 2 << 3 << std::endl << 5 << 6 << std::endl << 7 << 8 << std::endl; gives output [blah]123 [blah]56 [blah]78 Basically, I want a "[blah]" inserted at the front, then inserted after every non terminating std::endl ? The difficulty here is NOT the logic management, but detecting and overloading the handling of std::endl . Is there an elegant way to do this? Thanks! EDIT: I don't need advice on logic management. I need

问题 As I understand, the extraction operator skips the whitespace in the beginning and stops upon encountering a whitespace or end of stream. noskipws can be used to stop ignoring the leading whitespaces. I have the following program where I have used noskipws. #include <iostream> using namespace std; int main() { char name[128]; cout<<"Enter a name "; cin>>noskipws>>name; cout<<"You entered "<<name<<"\n"; cout<<"Enter another name "; cin>>name; cout<<"You entered "<<(int)name[0]<<"\n"; return 0;

问题 I am sorry that I duplicate this question, but I don't have the reputation required to comment there and the answers there are not convincing for me. #include<iostream> class my_ostream : public std::ostream { public: std::string prefix; my_ostream():prefix("*"){} my_ostream& operator<<(const std::string &s){ std::cout << this->prefix << s; return *this; } }; int main(){ my_ostream s; std::string str("text"); s << str << std::endl; } Here I get: no match for ‘operator<<’ in ‘s.my_ostream:

问题 I want to figure out how to pass a manipulator like std::endl to a function and then use the passed-in manipulator in the function. I can declare the function like this: void f(std::ostream&(*pManip)(std::ostream&)); and I can call it like this: f(std::endl); That's all fine. My problem is figuring out how to use the manipulator inside f . This doesn't work: void f(std::ostream&(*pManip)(std::ostream&)) { std::cout << (*pManip)(std::cout); // error } Regardless of compiler, the error message

问题 I've been looking around at various approaches to the problem of threadsafe logging, but I haven't seen anything quite like this, so I dunno if it's somehow awful that I haven't noticed due to being a complete newbie to C++, threads and iostreams. It seems to work in the basic tests I've put it through. Basically I have a Log class (creative, I know...) which has operator<< set up for the standard manipulators, so I can merrily pass in whatever I want. However, I am aware that something like: