This question already has answers here: Concatenating two std::vectors (26 answers) Closed 6 years ago. Assuming I have 2 standard vectors: vector<int> a; vector<int> b; Let’s also say the both have around 30 elements. How do I add the vector b to the end of vector a? The dirty way would be iterating through b … Read more
What is a segmentation fault? Is it different in C and C++? How are segmentation faults and dangling pointers related? 17 s 17 Segmentation fault is a specific kind of error caused by accessing memory that “does not belong to you.” It’s a helper mechanism that keeps you from corrupting the memory and introducing hard-to-debug … Read more
Here is the extract from the program in question. The matrix img[][] has the size SIZE×SIZE, and is initialized at: img[j][i] = 2 * j + i Then, you make a matrix res[][], and each field in here is made to be the average of the 9 fields around it in the img matrix. The … Read more
What are the C++ rules for calling the base class constructor from a derived class? For example, I know in Java, you must do it as the first line of the subclass constructor (and if you don’t, an implicit call to a no-arg super constructor is assumed – giving you a compile error if that’s … Read more
What is the correct (most efficient) way to define the main() function in C and C++ — int main() or void main() — and why? And how about the arguments? If int main() then return 1 or return 0? There are numerous duplicates of this question, including: What are the valid signatures for C’s main() … Read more
Why does the sizeof operator return a size larger for a structure than the total sizes of the structure’s members? 12 s 12 This is because of padding added to satisfy alignment constraints. Data structure alignment impacts both performance and correctness of programs: Mis-aligned access might be a hard error (often SIGBUS). Mis-aligned access might … Read more
What is the difference between “cache unfriendly code” and the “cache friendly” code? How can I make sure I write cache-efficient code? 9 s 9 Preliminaries On modern computers, only the lowest level memory structures (the registers) can move data around in single clock cycles. However, registers are very expensive and most computer cores have … Read more
In c++ what is object slicing and when does it occur? 18 s 18 Most answers here fail to explain what the actual problem with slicing is. They only explain the benign cases of slicing, not the treacherous ones. Assume, like the other answers, that you’re dealing with two classes A and B, where B … Read more
Recently I’ve bumped into a realization/implementation of the Singleton design pattern for C++. It has looked like this (I have adopted it from the real-life example): // a lot of methods are omitted here class Singleton { public: static Singleton* getInstance( ); ~Singleton( ); private: Singleton( ); static Singleton* instance; }; From this declaration, I … Read more
How do I concatenate two std::vectors? 26 s 26 vector1.insert( vector1.end(), vector2.begin(), vector2.end() );