stl

问题 Does anyone know an efficient way to right circular-shift a matrix? Btw, the matrix is binary but a method to solve a non-binary matrix is also fine. Right now, I'm thinking of implementing a circular array for the rows of my matrix and updating each row whenever a shift operation is required. Another method, I was considering was implementing a vector of pointers to columns (of the matrix) represented by vectors and swapping them around when a shift operation occurs. E.g. 1 2 3 4 5 6 7 8 9

问题 This has been running through my mind as a possible solution to an issue, however as it is a fairly obvious technical violation of something in C++, I wanted to know how likely to it is to fail, whether there is another fairly obvious approach, etc. I'm hoping this doesn't get into a flamewar about undefined behavior, but considering the topic I do expect a little bit. This is not the code I'm writing, I'm hoping it's not too simplified to not describe what I am attempting to do. class Code {

问题 How can I overload the STL implementation for methods like find, erase and insert to take varying parameters? I tried to look up the overloading of STL methods but couldn't find any help. 回答1: You can't overload the methods of a class without editing the code of that class. Write your own free functions that act as helpers; they would take the relevant container class as the first parameter. You can inherit from a class and add methods that way, but the std container classes are not designed

问题 I've a situation like the following, and I'm not sure whether or not the std::string elements of the struct leak memory or if this is ok. Is the memory allocated by those two std::strings deleted when free(v) is called? struct MyData { std::string s1; std::string s2; }; void* v = malloc(sizeof(MyData)); ... MyData* d = static_cast<MyData*>(v); d->s1 = "asdf"; d->s2 = "1234"; ... free(v); Leak or not? I'm using the void-pointer because I have another superior struct, which consists of an enum

问题 This question already has answers here : Erasing elements from a vector (5 answers) Closed 5 years ago . Here my code. I want remove from vector all elements with successfully called method 'release'. bool foo::release() { return true; } // ... vector<foo> vec; // ... remove_if(vec.begin(), vec.end(), [](foo & f) { return f.release() == true; }); // ... But remove_if not deleting all elements from vector vec . How remove_if works? 回答1: std::remove_if re-arranges the elements of the vector

问题 I am using a map inside a map and want to access a specific member in the second map. std::map<int, std::map<DWORD,IDLL::CClass*>*> MyMap 回答1: Try auto outerIt = MyMap.find(someInt); if(outerIt != MyMap.end()) { auto innerIt = (*outerIt)->find(someDWord); if(innerIt != (*outerIt)->end()) { auto yourElement = *innerIt; } } 回答2: If you are sure the keys exist, you could also try: IDLL::CClass* x = (*MyMap[key1])[key2]; 回答3: You can use std::map::find in two steps: first to find the value

问题 I want my map to be searchable and I want to be capable to kick out from it elements that were inserted into it longest time ago (with api like map.remove(map.get_iterator_to_oldest_inserted_element()) ) like mix of queqe and map.. Is there any such container in STL or Boost? 回答1: You can use boost::multi_index using the ordered_unique and sequence indices, as in this example. #include <iostream> #include <boost/multi_index_container.hpp> #include <boost/multi_index/ordered_index.hpp>

问题 This question already has answers here : Closed 11 years ago . Duplicate: What happens if you call erase on a map element while iterating from begin to end How to filter items from a stdmap I have a map map1<string,vector<string>> i have a iterator for this map "itr". i want to delete the entry from this map which is pointed by "itr". i can use the function map1.erase(itr); after this line the iterator "itr" becomes invalid. as per my requirement in my project,the iterator must point to the

问题 I have been following this convention thus far: std::string line; while(std::getline(in,line)) { if(line.size() && line[0] =='#') continue; /* parse text*/ } The obvious drawback is that comment may not begin at the first character, in the case of leading whitespace. What is the good way to deal with this sort of a thing? 回答1: Simple enhancement: you may want to use line.find_first_not_of(" ") to get the first non-whitespace and then check if that is a '#'. That would also cover to the zero

问题 I need to split a line based on two separators: ' ' and ; . By example: input : " abc ; def hij klm " output: {"abc","def","hij","klm"} How can I fix the function below to discard the first empty element? std::vector<std::string> Split(std::string const& line) { std::regex seps("[ ;]+"); std::sregex_token_iterator rit(line.begin(), line.end(), seps, -1); return std::vector<std::string>(rit, std::sregex_token_iterator()); } // input : " abc ; def hij klm " // output: {"","abc","def","hij","klm