C++ <array> data function

C++ container class <array>

datais a very special function in array, itReturns a pointer to the underlying array., allowing you to use array just like a C array.

dataIs a member function of the container class, used toreturns a pointer to the container's internal data storage. This enables array to interoperate with C-style APIs or other code that requires raw pointers.

dataprovides a bridge between array and C language code, reflecting array's compatibility.

Word Definitions： datameans "data", indicating obtaining the pointer to the underlying data.

Basic Syntax and Parameters

datais a member function of the container class, and calling it requires no parameters.

Syntax format

T* data();
const T* data() const;

Parameter description

  • Parameter: No parameters
    • dataIt does not accept any parameters.

Function description

  • Return Value: Returns a pointer to the underlying array.Pointer. If the container is a const container, a const pointer is returned.
  • Effect: The returned pointer points to the first element of the container, equivalent to&operator[](0)。
  • Note: array is fixed in size and never reallocates memory, thereforedata()The returned pointer is always valid.

Example

let us thoroughly master it through a series of examples.dataUsage.

Example 1: Basic usage - obtaining the underlying array pointer

Example

#include <iostream>
#include <array>

int main() {
    // 1. Create an array
    std::array<int, 5> numbers = {10, 20, 30, 40, 50};

    std::cout << "The size of array is: " << numbers.size() << std::endl;

    // 2. Use data to get the underlying array pointer
    int* ptr = numbers.data();

    std::cout << "Access through pointer: " << std::endl;
    for(size_t i = 0; i < numbers.size(); ++i) {
        std::cout << "ptr[" << i << "] = " << ptr[i] << std::endl;
    }

    return 0;
}

Expected Output:

array的大小是: 5
通过指针访问:
ptr[0] = 10
ptr[1] = 20
ptr[2] = 30
ptr[3] = 40
ptr[4] = 50

Code analysis:

  1. numbers.data()Returns a pointer to the first element.
  2. Through the returned pointer, all elements can be accessed using array subscript syntax.

Example 2: Modifying elements via pointer

dataThe returned pointer can be used to modify elements.

Example

#include <iostream>
#include <array>

int main() {
    std::array<int, 3> numbers = {10, 20, 30};

    std::cout << "Before modification: ";
    for(int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    // Get the pointer through data() and modify elements
    int* ptr = numbers.data();
    ptr[0] = 100;
    ptr[1] = 200;
    ptr[2] = 300;

    std::cout << "After modification: ";
    for(int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;

    return 0;
}

Expected Output:

修改前: 10 20 30
修改后: 100 200 300

Code analysis:

  • Throughdata()The returned pointer can directly modify array's internal data.

Example 3: Interacting with C-style APIs

dataone of its main uses is to interact with C functions that require array pointers.

Example

#include <iostream>
#include <array>

// A hypothetical C-style function that computes the sum of an array
int sumArray(const int* arr, size_t size) {
    int sum = 0;
    for(size_t i = 0; i < size; ++i) {
        sum += arr[i];
    }
    return sum;
}

int main() {
    std::array<int, 5> numbers = {1, 2, 3, 4, 5};

    // Use data() to pass the array to a C-style function
    int total = sumArray(numbers.data(), numbers.size());

    std::cout << "Array elements: ";
    for(int n : numbers) {
        std::cout << n << " ";
    }
    std::cout << std::endl;
    std::cout << "Sum: " << total << std::endl;

    return 0;
}

Expected Output:

数组元素: 1 2 3 4 5
总和: 15

Code analysis:

  • numbers.data()Pass the array's internal array pointer to functions that acceptconst int*of the function.
  • This demonstrates array's ability to interact seamlessly with C code.

C++ container class <array>

other extensions