First, make an ifstream: #include <fstream> std::ifstream infile(“thefile.txt”); The two standard methods are: Assume that every line consists of two numbers and read token by token: int a, b; while (infile >> a >> b) { // process pair (a,b) } Line-based parsing, using string streams: #include <sstream> #include <string> std::string line; while (std::getline(infile, line)) … Read more
In alphabetical order: std::string name = “John”; int age = 21; std::string result; // 1. with Boost result = name + boost::lexical_cast<std::string>(age); // 2. with C++11 result = name + std::to_string(age); // 3. with FastFormat.Format fastformat::fmt(result, “{0}{1}”, name, age); // 4. with FastFormat.Write fastformat::write(result, name, age); // 5. with the {fmt} library result = fmt::format(“{}{}”, … Read more
You can use std::find from <algorithm>: #include <algorithm> #include <vector> vector<int> vec; //can have other data types instead of int but must same datatype as item std::find(vec.begin(), vec.end(), item) != vec.end() This returns an iterator to the first element found. If not present, it returns an iterator to one-past-the-end. With your example: #include <algorithm> #include … Read more
The main reason is that classic C casts make no distinction between what we call static_cast<>(), reinterpret_cast<>(), const_cast<>(), and dynamic_cast<>(). These four things are completely different. A static_cast<>() is usually safe. There is a valid conversion in the language, or an appropriate constructor that makes it possible. The only time it’s a bit risky is … Read more
In C++11, you can do this with standard library facilities: #include <chrono> #include <thread> std::this_thread::sleep_for(std::chrono::milliseconds(x)); Clear and readable, no more need to guess at what units the sleep() function takes.
Basic meaning and syntax Both keywords can be used in the declaration of objects as well as functions. The basic difference when applied to objects is this: const declares an object as constant. This implies a guarantee that once initialized, the value of that object won’t change, and the compiler can make use of this … Read more
a.insert(a.end(), b.begin(), b.end()); or a.insert(std::end(a), std::begin(b), std::end(b)); The second variant is a more generically applicable solution, as b could also be an array. However, it requires C++11. If you want to work with user-defined types, use ADL: using std::begin, std::end; a.insert(end(a), begin(b), end(b));
The difference is caused by the same super-alignment issue from the following related questions: Why is transposing a matrix of 512×512 much slower than transposing a matrix of 513×513? Matrix multiplication: Small difference in matrix size, large difference in timings But that’s only because there’s one other problem with the code. Starting from the original … Read more
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 memory bugs. Whenever you get a segfault you know you are doing something wrong with memory – accessing a variable that has already … Read more
The return value for main indicates how the program exited. Normal exit is represented by a 0 return value from main. Abnormal exit is signaled by a non-zero return, but there is no standard for how non-zero codes are interpreted. As noted by others, void main() is prohibited by the C++ standard and should not … Read more