Which functions in STL can use C++ function objects?

STL provides several functions that accept C function objects as parameters and are used to operate collections or perform specific transformations. These functions include: transform(): Transforms the elements of the collection using the specified function object. for_each(): Performs an operation on each element in the collection, using the specified function object. sort(): Sorts the collection according to the specified comparison function object. find_if(): Find elements that meet the specified conditions (defined by the function object). count_if(): Counts the number of elements that meet the specified conditions (defined by the function object).

Functions in STL that can use C function objects

There are several functions in STL (Standard Template Library) that can accept C function objects as parameters. These functions are typically used to manipulate collections or perform specific transformations. Here are a few common examples:

• transform(): Converts a series of elements to another series of elements, using the specified function object as the conversion function.
• for_each(): Perform an operation on each element in the collection, using the specified function object.
• sort(): Sort the collection according to the specified comparison function object.
• find_if(): Find elements in the collection that meet the specified conditions (defined by the function object).
• count_if(): Count the number of elements in the set that meet the specified conditions (defined by the function object).

Practical case

The following code example demonstrates how to use the transform() function object to convert a number to a string:

#include <algorithm>
#include <iostream>
#include <vector>
#include <string>

using namespace std;

int main() {
  // 创建一个数字向量
  vector<int> numbers = {1, 2, 3, 4, 5};

  // 定义一个将数字转换为字符串的函数对象
  struct IntToString {
    string operator()(int num) const {
      return to_string(num);
    }
  };

  // 使用 transform() 将数字向量转换为字符串向量
  vector<string> strings;
  transform(begin(numbers), end(numbers), back_inserter(strings), IntToString());

  // 打印字符串向量
  for (const auto &str : strings) {
    cout << str << endl;
  }

  return 0;
}

In this example, the IntToString function object defines an operator () that converts an integer to a string. The transform() function uses this as a transformation function to convert a numeric vector into a string vector.

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