C++ language note

Post by ailswan Sep. 12, 2023

C++ language note

Date: September 12, 2023 Tags: c++ language

Summary

This document provides a list of common C++ methods, functions, and features spanning categories like string manipulation, vector operations, and more.

String Methods:

  • s.substr(pos, len): Get a substring.
  • s.find(sub): Find a substring.
  • s.replace(pos, len, new_sub): Replace substring.
  • s.c_str(): Convert to C-style string.
  • s.size(): Get string size.

Vector Methods:

  • vec.push_back(item): Add item to vector.
  • vec.insert(pos, item): Insert item at position.
  • vec.erase(pos): Remove item at position.
  • vec.size(): Return vector size.
  • vec.begin(), vec.end(): Return iterators.
  • vec.front(): Access first element.
  • vec.back(): Access last element.
  • vec.assign(first, last): Assign a range of elements to the vector.

Set Methods:

  • set.insert(item): Add item to set.
  • set.erase(item): Remove item from set.
  • set.find(item): Find item in set.
  • set.size(): Return set size.

Map Methods:

  • map[key]: Access value associated with the key.
  • map.insert(pair): Insert key-value pair.
  • map.erase(key): Remove key-value pair.
  • map.find(key): Find value by key.

Looping Techniques:

  • for(auto &item : container): Range-based for loop.

I/O Streams:

  • cin >> variable: Read from standard input.
  • cout << "text" << variable: Write to standard output.
  • cerr << "error message": Write to standard error.

Memory Management:

  • new Type: Allocate memory.
  • delete pointer: Deallocate memory.
  • new Type[]: Allocate array.
  • delete[] pointer: Deallocate array.

Lambda Functions:

  • [capture](parameters) -> return_type { body }: Define a lambda function.

STL Algorithms:

  • std::sort(begin, end): Sort elements.
  • std::find(begin, end, value): Find element.
  • std::count(begin, end, value): Count occurrences.
  • std::binary_search(begin, end, value): Check if a value exists in a sorted range.

Noteworthy Differences:

In-Place vs. Return Value:

  • In C++, most operations on containers like vectors or strings are in-place.

String Operations:

Strings in C++ (std::string) are mutable. This is unlike strings in languages like Python or Java.

Looping Techniques:

  • for(auto &item : container): Range-based for loop.
  • Accessing it->first in a map iteration.

Memory Management:

In C++, developers have control over memory allocation and deallocation using new and delete. This requires extra care to prevent memory leaks.

Lambda Functions in Different Scenarios:

  1. Sort with custom comparator: 
    • std::sort(vec.begin(), vec.end(), [](int a, int b) { return a > b; });
  2. Find first odd number in a vector: 
    • auto it = std::find_if(vec.begin(), vec.end(), [](int n) { return n % 2 != 0; });

Math Functions:

std::max and std::min:

  • std::max(a, b): Returns the greater of the two values a and b.
  • std::min(a, b): Returns the smaller of the two values a and b.

Algorithmic Operations:

std::accumulate:

  • std::accumulate(begin, end, initial): Computes the sum of a range of elements.

std::transform:

  • std::transform(begin1, end1, begin2, result, binary_operation): Applies a binary operation to pairs of elements from two ranges and stores the result in a third range.

std::reverse:

  • std::reverse(begin, end): Reverses the order of elements in a range.

Example Usage:

```cpp #include #include

// Example usage of std::max and std::min int main() { int a = 5, b = 8; int max_result = std::max(a, b); int min_result = std::min(a, b);

int arr[] = {1, 2, 3, 4, 5};
int sum = std::accumulate(std::begin(arr), std::end(arr), 0);

std::vector<int> input = {1, 2, 3, 4, 5};
std::vector<int> output(input.size());
std::transform(input.begin(), input.end(), output.begin(), [](int x) { return x * 2; });

std::reverse(input.begin(), input.end());

return 0; }