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C++ is a very popular and powerful language which includes all the low-level features of [[C_(programming_language) | C]] (e.g. pointers, operator overloading) along many high-level features (regex, STL containers) thanks to the C++ standard library.<br> | |||
Some people may think of it as an object-oriented version of C. | |||
==Usage== | ==Usage== | ||
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===Syntax=== | ===Syntax=== | ||
====Main==== | |||
All C++ programs launch in a <code>main</code> function. | |||
Similar to [[C]], the arguments are <code>int argc</code> and <code>char *argv[]</code>. | |||
These can be easily converted to a <code>std::vector<std::string></code> for convenience. | |||
<syntaxhighlight lang="cpp"> | |||
#include <string> | |||
#include <vector> | |||
int main(int argc, char *argv[]) { | |||
std::vector<std::string> args(argv, argv + argc); | |||
// Your code here | |||
return EXIT_SUCCESS; | |||
} | |||
</syntaxhighlight> | |||
====Headers==== | |||
[https://stackoverflow.com/questions/10694255/cmath-vs-math-h-and-similar-c-prefixed-vs-h-extension-headers Reference] | |||
C++ includes C-headers such as <code>math.h</code> and <code>cmath</code>.<br> | |||
The C-style header will place everything in the global namespace while the C++ header will place everything in <code>std</code>.<br> | |||
You should use <code>cmath</code>. | |||
====Lambda Expressions==== | ====Lambda Expressions==== | ||
[https://en.cppreference.com/w/cpp/language/lambda Reference] | [https://en.cppreference.com/w/cpp/language/lambda Reference] | ||
====Casting==== | ====Casting==== | ||
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This will allocate an array in the heap.<br> | This will allocate an array in the heap.<br> | ||
[https://shendrick.net/Coding%20Tips/2015/03/15/cpparrayvsvector.html array vs vector] | [https://shendrick.net/Coding%20Tips/2015/03/15/cpparrayvsvector.html array vs vector]<br> | ||
If you need a static sized array, you can use <code>std::array</code> in the <code>array</code> header.<br> | If you need a static sized array, you can use <code>std::array</code> in the <code>array</code> header.<br> | ||
This wrapper around C-style arrays gives us size information and allows the array to be passed around by reference while keeping the array on the stack unlike <code>std::vector</code>.<br> | This wrapper around C-style arrays gives us size information and allows the array to be passed around by reference while keeping the array on the stack unlike <code>std::vector</code>.<br> | ||
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#include <cerrno> | #include <cerrno> | ||
std::string get_file_contents( | std::string get_file_contents(std::string filename) | ||
{ | { | ||
std::ifstream in(filename, std::ios::in | std::ios::binary); | std::ifstream in(filename, std::ios::in | std::ios::binary); | ||
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in.seekg(0, std::ios::beg); | in.seekg(0, std::ios::beg); | ||
in.read(&contents[0], contents.size()); | in.read(&contents[0], contents.size()); | ||
return contents; | |||
return | |||
} | } | ||
throw(errno); | throw(errno); | ||
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Use <code>shared_ptr</code> when multiple objects need to reference the same thing.<br> | Use <code>shared_ptr</code> when multiple objects need to reference the same thing.<br> | ||
Use <code>weak_ptr</code> to avoid cyclic dependencies which cause issues with reference counting.<br> | Use <code>weak_ptr</code> to avoid cyclic dependencies which cause issues with reference counting.<br> | ||
If you are using C++14 or newer, you should use <code>make_unique</code> or <code>make_shared</code> which will only make one memory allocation for both the object and the pointer rather than two memory allocations.<br> | |||
Alternatively if you already have a smart pointer, you can call <code>my_ptr.reset(new Car())</code> to change the pointer or <code>my_ptr.reset()</code> to deallocate the object referenced by the pointer. | |||
Example: | Example: | ||
<syntaxhighlight lang="cpp"> | <syntaxhighlight lang="cpp"> | ||
// Block-scope car | |||
Car my_car; | |||
// Old C++ | |||
// Must call delete my_car; to avoid memory leaks. | |||
Car *my_car = new Car(); | |||
// Using unique ptr | |||
std::unique_ptr<Car> my_car(new Car()); | std::unique_ptr<Car> my_car(new Car()); | ||
// Or starting from C++14 | // Or starting from C++14 | ||
auto my_car = std::make_unique<Car>(); | auto my_car = std::make_unique<Car>(); | ||
</syntaxhighlight> | </syntaxhighlight> | ||
Note: If the object you need is not very large, you can consider just including it as part of your class (or leaving it on the stack) rather than use pointers. | |||
====Garbage Collection==== | ====Garbage Collection==== | ||
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There are a few ways to do this: | There are a few ways to do this: | ||
* Use smart pointers | * Use smart pointers | ||
* | * Swap | ||
* Call a clear/shrink/deallocate function | * Call a clear/shrink/deallocate function | ||
Example [https://stackoverflow.com/questions/3054567/right-way-to-deallocate-an-stdvector-object Reference]: | Example [https://stackoverflow.com/questions/3054567/right-way-to-deallocate-an-stdvector-object Reference]: | ||
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my_vector.reset(); | my_vector.reset(); | ||
// | // Swap | ||
std::vector<float> my_vector(99); | std::vector<float> my_vector(99); | ||
std::vector<float>().swap(my_vector); | my_vector = std::vector<float>; | ||
// Or alternatively | |||
// std::vector<float>().swap(my_vector); | |||
// | // Swap for cl::Buffer | ||
cl::Buffer my_buf(context, CL_MEM_READ_WRITE, size); | cl::Buffer my_buf(context, CL_MEM_READ_WRITE, size); | ||
my_buf = cl::Buffer(); | |||
// Clear and shrink | // Clear and shrink | ||
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</syntaxhighlight> | </syntaxhighlight> | ||
==Containers== | ==STL== | ||
===unordered_set=== | STL is the Standard Template Library.<br> | ||
STL can either refer to the 1994 original STL implementation by Stepanov and Lee from HP or the general set of algorithms, containers, functions, and iterators.<br> | |||
Many STL containers are now built into the standard library (std) of C++.<br> | |||
This section focuses only on the portions of STL which have been incorporated into the C++ standard library. | |||
===Simple Containers=== | |||
====std::pair==== | |||
===Sequences=== | |||
====std::vector==== | |||
====std::list==== | |||
===Container adaptors=== | |||
====std::queue==== | |||
====std::stack==== | |||
===Associative Containers=== | |||
Also known as maps or associative arrays. | |||
====std::unordered_set==== | |||
<code>#include <unordered_set></code><br> | <code>#include <unordered_set></code><br> | ||
This is a hashset.<br> | This is a hashset.<br> | ||
<syntaxhighlight lang="cpp> | <syntaxhighlight lang="cpp> | ||
unordered_set<int> my_set; | std::unordered_set<int> my_set; | ||
// add things to myset | // add things to myset | ||
my_set.insert(5); | my_set.insert(5); | ||
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my_set.find(5) != my_set.end(); | my_set.find(5) != my_set.end(); | ||
</syntaxhighlight> | </syntaxhighlight> | ||
====std::unordered_map==== | |||
==Boost== | |||
==Programming Styles== | ==Programming Styles== | ||
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[https://gist.github.com/bkaradzic/2e39896bc7d8c34e042b Reference]<br> | [https://gist.github.com/bkaradzic/2e39896bc7d8c34e042b Reference]<br> | ||
Somewhat opposite of modern C++.<br> | Somewhat opposite of modern C++.<br> | ||
Basically only use C++ for its classes. Do everything else C-style. | Also known as "C with Classes"<br> | ||
Basically only use C++ for its classes. Do everything else C-style.<br> | |||
The main benefit is compatibility with older compilers/libraries and easier understanding for people less familiar with newer C++ features. | The main benefit is compatibility with older compilers/libraries and easier understanding for people less familiar with newer C++ features. | ||
*Don't use C++ runtime wrapper for C runtime includes (<cstdio>, <cmath>, etc.), use C runtime instead (<stdio.h>, <math.h>, etc.) | * Don't use C++ runtime wrapper for C runtime includes (<cstdio>, <cmath>, etc.), use C runtime instead (<stdio.h>, <math.h>, etc.) | ||
*Don't use stream (<iostream>, <stringstream>, etc.), use printf style functions instead. | * Don't use stream (<iostream>, <stringstream>, etc.), use printf style functions instead. | ||
*Don't use anything from STL that allocates memory, unless you don't care about memory management. | * Don't use anything from STL that allocates memory, unless you don't care about memory management. | ||
* Don't use exceptions. | |||
* Don't use RTTI. | |||
== | ==Useful Libraries== | ||
== | A list of useful libraries | ||
===cxxopts=== | |||
[https://github.com/jarro2783/cxxopts Link]<br> | |||
A header-only C++ argument parser.<br> | |||
Note that if you already use Boost, you can use <code>Boost::Program_options</code> instead. | |||
===Eigen=== | |||
{{main | Eigen (C++ library)}} | |||
A C++ linear algebra library. |