C++ <array> fill function
fillis used in array toFill all elementsA function that can quickly set all elements to the same value.
fillis a member function of the container class, used toSet all elements in the container to the specified value.This is an O(n) operation that requires iterating through all elements.
fillIs a shortcut for initializing or resetting the array.
Word Definitions： fillMeans "fill", i.e., setting all elements to a specified value.
Basic syntax and parameters
fillIs a member function of the container class, requiring a specified fill value.
Syntax format
void fill(const T& value);
Parameter description
- Parameter：
value- Type: same as the container element type
- Description: The value to fill into all elements.
Function description
- Return Value：
void(No return value). - Effect: Set every element in the container to
value。 - Note：
fillmodifies all elements in the container.
Example
Let us thoroughly master through a series of examples.fillUsage.
Example 1: Basic usage - filling with the same value
Example
#include <array>
int main() {
std::array<int, 5> numbers = {1, 2, 3, 4, 5};
std::cout << "Before fill: ";
for(int n : numbers) {
std::cout << n << " ";
}
std::cout << std::endl;
// Fill all elements with 0
numbers.fill(0);
std::cout << "After fill: ";
for(int n : numbers) {
std::cout << n << " ";
}
std::cout << std::endl;
return 0;
}
Expected run result:
填充前: 1 2 3 4 5 填充后: 0 0 0 0 0
Code analysis:
numbers.fill(0)Set all 5 elements to 0.- This is an O(n) operation, traversing all elements and assigning values.
Example 2: Initializing to a specific value
Usagefillcan quickly initialize an array.
Example
#include <array>
#include <string>
int main() {
// Create and initialize to -1
std::array<int, 10> scores;
scores.fill(-1);
std::cout << "Initialized to -1: ";
for(int s : scores) {
std::cout << s << " ";
}
std::cout << std::endl;
// Create and initialize to empty string
std::array<std::string, 3> names;
names.fill("Unknown");
std::cout << "Initialized to Unknown: ";
for(const auto& n : names) {
std::cout << n << " ";
}
std::cout << std::endl;
return 0;
}
Expected run result:
初始化为 -1: -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 初始化为 Unknown: Unknown Unknown Unknown
Code analysis:
fillCan be used to quickly initialize an array of any type.- For integers, 0 or -1 is commonly used; for strings, an empty string or specific placeholder is commonly used.
Example 3: Resetting the array
fillcan be used to reset the array to its initial state.
Example
#include <array>
int main() {
std::array<int, 5> buffer;
// Initialize to 1-5
for(int i = 0; i < 5; ++i) {
buffer[i] = i + 1;
}
std::cout << "Initial data: ";
for(int n : buffer) std::cout << n << " ";
std::cout << std::endl;
// Simulate resetting after using buffer
buffer.fill(0);
std::cout << "After reset: ";
for(int n : buffer) std::cout << n << " ";
std::cout << std::endl;
return 0;
}
Expected run result:
初始数据: 1 2 3 4 5 重置后: 0 0 0 0 0
Code analysis:
fillCan quickly reset the array to a known state.- This is useful when the same buffer needs to be used multiple times.
Example 4: Using fill with std::generate
fillused in conjunction with STL algorithms.
Example
#include <array>
#include <algorithm>
int main() {
std::array<int, 10> numbers;
// Use fill to populate initial values
numbers.fill(1);
std::cout << "After fill 1: ";
for(int n : numbers) std::cout << n << " ";
std::cout << std::endl;
// Increment each element
for(auto& n : numbers) {
n *= 2;
}
std::cout << "After doubling: ";
for(int n : numbers) std::cout << n << " ";
std::cout << std::endl;
return 0;
}
Code analysis:
fillused to set initial values.- Afterwards, it can be further processed with loops or algorithms.
other extensions