C++ flat_map::begin() Function

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The std::flat_map::begin() function in C++, is used to return an iterator pointing to the first element of the flat_map container. It allows iteration from the start, making it useful for traversal and modifications.

This function comes in both const and non-const versions, ensuring the compatibility with read-only and modifiable access.

Syntax

Following is the syntax for std::flat_map::begin() function.

iterator begin() noexcept;
or
const_iterator begin() const noexcept;

Parameters

It does not accepts any parameter.

Return Value

This function returns the iterator to the first element.

Example 1

Let's look at the following example, where we are going to consider the basic usage of the begin() function.

#include 
#include 
#include 
int main() {
   boost::container::flat_map < int, std::string > a = {
      {1,"Hi"},
      {2,"Hello"},
      {3,"Welcome"}
   };
   auto x = a.begin();
   std::cout << "Result : " << x -> first << " -> " << x -> second << std::endl;
   return 0;
}

Output

Output of the above code is as follows −

Result : 1 -> Hi

This example modifies the first element using the iterator returned by begin(). cpp Copy Edit

Example 2

Consider the following example, where we are going to modify the first element using the iterator returned by the begin().

#include 
#include 
#include 
int main() {
   boost::container::flat_map < int, std::string > x = {
      {1,"RX100"},
      {2,"CIAZ"},
      {3,"CRUZE"}
   };
   auto a = x.begin();
   a -> second = "AUDI";
   std::cout << "Result : " << a -> first << " -> " << a -> second << std::endl;
   return 0;
}

Output

Following is the output of the above code −

Result : 1 -> AUDI