Detailed explanation of C++ function optimization: How to optimize space complexity?

Reduce the space complexity of C functions through the following techniques: use smart pointers, pass references instead of copies, use constant references, pass values ​​instead of pointers, and optimize container size. By using practical techniques such as smart pointers and transferring token ownership, unnecessary memory usage can be reduced and space efficiency improved.

Detailed explanation of C function optimization: techniques for optimizing space complexity

Introduction

Function optimization is an important strategy to improve the performance of C programs. Optimizing space complexity is crucial because it reduces memory usage and improves program execution efficiency. This article will introduce techniques for optimizing the space complexity of C functions and provide practical cases for illustration.

Optimization tips

1. Use smart pointers

Smart pointers can automatically manage heap memory and release the objects pointed to by the pointers. , to avoid memory leaks and optimize space usage. Such as std::unique_ptr and std::shared_ptr etc.

2. Pass reference instead of copy

When passing large objects or strings, passing reference instead of copy can avoid unnecessary memory copying and save space. For example:

void process(string& str);

3. Use constant references

Using const references can save space and prevent the value of the referenced object from being modified. For example:

void print(const string& str);

4. Pass values ​​instead of pointers

If the function does not need to modify parameters, you can pass values ​​instead of pointers to reduce memory usage. For example:

int sum(int n); // 传递值
int avg(int* nums); // 传递指针

5. Optimize container size

Pre-allocating the size of the container can prevent multiple memory reallocations and optimize space usage. Use the reserve() method to preallocate space. For example:

vector<int> nums;
nums.reserve(100); // 预分配 100 个元素

Practical case

Optimizing the space complexity of string processing functions

Consider a string that is Function to comma-separate a vector of strings:

vector<string> split(const string& str) {
  vector<string> tokens;
  size_t start = 0, end = 0;
  while ((end = str.find(',', start)) != string::npos) {
    tokens.push_back(str.substr(start, end - start));
    start = end + 1;
  }
  tokens.push_back(str.substr(start));
  return tokens;
}

This function requires creating a copy for each new string in the loop. The optimization method is as follows:

vector<string> split(const string& str) {
  vector<string> tokens;
  string token;
  size_t start = 0, end = 0;
  while ((end = str.find(',', start)) != string::npos) {
    token = str.substr(start, end - start);
    tokens.push_back(std::move(token)); // 传递 token 的拥有权
    start = end + 1;
  }
  token = str.substr(start);
  tokens.push_back(std::move(token));
  return tokens;
}

By using std::move(), the ownership of token is passed to tokens to avoid unnecessary The copy creation optimizes the space complexity.

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