How to concatenate a std::string and an int
I thought this would be really simple, but it’s presenting some difficulties. If I have How do I combine them to get a single string “John21”?
C++
C++ Singleton design pattern
In 2008 I provided a C++98 implementation of the Singleton design pattern that is lazy-evaluated, guaranteed-destruction, not-technically-thread-safe:Can any one provide me a sample of Singleton in c++? Here is an updated C++11 implementation of the Singleton design pattern that is lazy-evaluated, correctly-destroyed, and thread-safe. See this article about when to use a singleton: (not often)Singleton: How … Read more
How to track down a “double free or corruption” error
If you’re using glibc, you can set the MALLOC_CHECK_ environment variable to 2, this will cause glibc to use an error tolerant version of malloc, which will cause your program to abort at the point where the double free is done. You can set this from gdb by using the set environment MALLOC_CHECK_ 2 command before running your program; the program … Read more
Read file line by line using ifstream in C++
First, make an ifstream: 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)) { std::istringstream iss(line); int a, b; if … Read more
Remove secure warnings (_CRT_SECURE_NO_WARNINGS) from projects by default in Visual Studio
It may have been because I am still new to VS and definitely new to C, but the only thing that allowed me to build was adding At the top of my file, this suppressed the C4996 error I was getting with sprintf A bit annoying but perfect for my tiny bit of code and … Read more
how to implement quick sort algorithm in C++
Your consideration is wrong. The value of r does not change, since it is given as value to the Quicksort function(not a reference). You handle the ranges with p,q such that p is the first index in the range and q the first index not in the range. Thus, your calls were wrong: Here is the complete example. I used std::swap to change elements and ans std::vector … Read more
error: expected unqualified-id error: Meaning and fix? [duplicate]
As stated by @user657267 get rid of the semicolons when declaring a function and its implementation. If you were to have above the main and the implementation of that function below the main That would be ok. The implementation can also go above the main and then you don’t have to write the first line … Read more
How to fix C++ error: expected unqualified-id
There should be no semicolon here: …but there should be one at the end of your class definition:
‘g++’ is not recognized as an internal or external command, operable program or batch file
Try to set g++ to your system path. You can refer to this: http://stephencoakley.com/2015/01/21/guide-setting-up-a-simple-c-development-environment-on-windows
C++ Error: “Expression must have integral or enum type” [duplicate]
The error is clear. You can only use integral types (integer, enum, char etc. which are convertible to integral value), or any expression that evaluates to an integral type in switch statement.