C++

Does a const reference class member prolong the life of a temporary?

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Why does this: #include <string> #include <iostream> using namespace std; class Sandbox { public: Sandbox(const string& n) : member(n) {} const string& member; }; int main() { Sandbox sandbox(string(“four”)); cout << “The answer is: ” << sandbox.member << endl; return 0; } Give output of: The answer is: Instead of: The answer is: four 6 … Read more

OpenCV C++/Obj-C: Detecting a sheet of paper / Square Detection

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I successfully implemented the OpenCV square-detection example in my test application, but now need to filter the output, because it’s quite messy – or is my code wrong? I’m interested in the four corner points of the paper for skew reduction (like that) and further processing … Input & Output: Original image: click Code: double angle( … Read more

Is the order of iterating through std::map known (and guaranteed by the standard)?

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What I mean is – we know that the std::map‘s elements are sorted according to the keys. So, let’s say the keys are integers. If I iterate from std::map::begin() to std::map::end() using a for, does the standard guarantee that I’ll iterate consequently through the elements with keys, sorted in ascending order? Example: std::map<int, int> map_; … Read more

fork() branches more than expected?

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Consider the following piece of code: #include <stdio.h> #include <sys/types.h> #include <unistd.h> int main(void) { int i; for(i = 0; i < 2; i++) { fork(); printf(“.”); } return 0; } This program outputs 8 dots. How can that be possible? Should not there be 6 dots instead? 3 Answers 3

“Undefined reference to” template class constructor [duplicate]

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This question already has answers here: Why can templates only be implemented in the header file? (17 answers) Closed 7 years ago. I have no idea why this is happenning, since I think I have everything properly declared and defined. I have the following program, designed with templates. It’s a simple implementation of a queue, … Read more