std

问题 I wrote a short testprogram to see if I can append to a string using stringstream repeatedly. In the first version I got Output1 and I don't really understand why s1 stays empty. I found out that I have to do ss.clear() and then get the expected result in Output2. Can anybody explain why it doesn't work without the clear? I would have expected that, If I repeatedly enter numbers and fetch them back into a string, I should get always the number. I was unsure if the number gets appended, but

问题 I just encountered a weird error which saying that find is not a member of std. error C2039: 'find' : is not a member of 'std' error C3861: 'find': identifier not found Basically, I want to find whether a string can be found in the vector Any idea why does this happen? the code assist tells me that there is find method in std. so this is basically what I did : #include "OperatorUtil.h" #include <iostream> #include <string> #include <stdlib.h> #include <math.h> #include <sstream> using

问题 This question already has answers here : Closed 6 years ago . Possible Duplicate: std::vector resize downward If I resize() an std::vector to some size smaller than its current size, is it possible that the vector will ever allocate new memory? This is important to me for performance reasons. 回答1: No, resize ing to a smaller size will never reallocate. In case the container shrinks, all iterators, pointers and references to elements that have not been removed remain valid after the resize and

问题 This does not work. I'm trying to learn how to use std::copy but I can't find any working code. I ran this in gcc 4.6.1. And it does not do anything when I hit control D. If I hit Control C...it prints out the new lines only. Found code here: Printing an array in C++? #include <iostream> #include <vector> #include <algorithm> #include <iterator> int main() { std::vector<int> userInput; // Read until end of input. // Hit control D std::copy(std::istream_iterator<int>(std::cin), std::istream

问题 I coded the following function to convert a std::vector of uint8_t to an ascii hexadecimal string (gnu++98 standard). ... string uint8_vector_to_hex_string(const vector<uint8_t>& v) { stringstream ss; vector<uint8_t>::const_iterator it; for (it = v.begin(); it != v.end(); it++) { char hex_char[2]; sprintf(hex_char, "%x", *it); ss << "\\x" << hex_char; } return ss.str(); } ... It works fine. I was wondering if there is a better way to do this transformation, maybe using not both the

问题 I want to remove element from queue with specific value. How to do such thing? (I am trying to create a concurrent mixture of map and queue and currently I try to implement on this answer) So I currently have such code: #ifndef CONCURRENT_QUEUED_MAP_H #define CONCURRENT_QUEUED_MAP_H #include <map> #include <deque> #include <boost/thread.hpp> #include <boost/thread/locks.hpp> template <class map_t_1, class map_t_2> class concurrent_queued_map { private: std::map<map_t_1, map_t_2> _ds; std:

问题 I want to remove element from queue with specific value. How to do such thing? (I am trying to create a concurrent mixture of map and queue and currently I try to implement on this answer) So I currently have such code: #ifndef CONCURRENT_QUEUED_MAP_H #define CONCURRENT_QUEUED_MAP_H #include <map> #include <deque> #include <boost/thread.hpp> #include <boost/thread/locks.hpp> template <class map_t_1, class map_t_2> class concurrent_queued_map { private: std::map<map_t_1, map_t_2> _ds; std:

问题 I am trying to remove elements from a std::list and keep some stats of deleted elements. In order to do so, I use the remove_if function from the list, and I have a predicate. I would like to use this predicate to gather statistics. Here is the code for the predicate: class TestPredicate { private: int limit_; public: int sum; int count; TestPredicate(int limit) : limit_(limit), sum(0), count(0) {} bool operator() (int value) { if (value >= limit_) { sum += value; ++count; // Part where I

问题 Consider this code: #include <iostream> template<class C> struct time { }; int main() { } It produces (GCC 4.5): error: ‘template<class C> struct time’ redeclared as different kind of symbol /usr/include/time.h:186:15: error: previous declaration of ‘time_t time(time_t*)’ Why does iostream include time_t time(time_t*) ? Why does iostream include time_t time(time_t*) outside std namespace? (unanswered) Why, if I remove template<class C> , do I not get this error? 回答1: If you run g++ -H -Wall

问题 What is the result of std::wstring.length() function, the length in wchar_t(s) or the length in symbols? And why? TCHAR r2[3]; r2[0] = 0xD834; // D834, DD1E - musical G clef r2[1] = 0xDD1E; // r2[2] = 0x0000; // '/0' std::wstring r = r2; std::cout << "capacity: " << r.capacity() << std::endl; std::cout << "length: " << r.length() << std::endl; std::cout << "size: " << r.size() << std::endl; std::cout << "max_size: " << r.max_size() << std::endl; Output> capacity: 351 length: 2 size: 2 max