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Showing content from https://en.cppreference.com/w/cpp/language/../error/error_code/../../iterator/size.html below:

std::size, std::ssize - cppreference.com

Returns the size of the given range.

1,2) Returns c.size(), converted to the return type if necessary.

3,4) Returns N.

[edit] Parameters c - a container or view with a size member function array - an array of arbitrary type [edit] Return value

1) c.size()

3,4) N

[edit] Exceptions

1,2) May throw implementation-defined exceptions.

[edit] Overloads

Custom overloads of size may be provided for classes and enumerations that do not expose a suitable size() member function, yet can be detected.

[edit] Possible implementation [edit] Notes [edit] Example

#include <cassert>
#include <cstring>
#include <iostream>
#include <vector>
 
int main()
{
    // Works with containers
    std::vector<int> v{3, 1, 4};
    assert(std::size(v) == 3);
 
    // And works with built-in arrays too
    int a[]{-5, 10, 15};
    // Returns the number of elements (not bytes) as opposed to sizeof
    assert(std::size(a) == 3);
    std::cout << "size of a[]: " << sizeof a << '\n'; // 12, if sizeof(int) == 4
 
    // Provides a safe way (compared to sizeof) of getting string buffer size
    const char str[] = "12345";
    // These are fine and give the correct result
    assert(std::size(str) == 6);
    assert(sizeof(str) == 6);
 
    // But use of sizeof here is a common source of bugs
    const char* str_decayed = "12345";
    // std::cout << std::size(str_decayed) << '\n'; // Usefully fails to compile
    std::cout << sizeof(str_decayed) << '\n'; // Prints the size of the pointer!
 
    // Since C++20 the signed size (std::ssize) is available
    auto i = std::ssize(v);
    for (--i; i != -1; --i)
        std::cout << v[i] << (i ? ' ' : '\n');
    assert(i == -1);
 
    // Note that the string literal includes the ending null character, which
    // will be part of the constructed characters array. This makes std::size
    // behave differently from std::strlen and std::string::size:
    constexpr char symbols[] = "0123456789";
 
    static_assert(std::size(symbols) == 11);
    static_assert(std::string(symbols).size() == 10);
    assert(std::strlen(symbols) == 10);
}

Possible output:

[edit] See also signed integer type returned when subtracting two pointers
(typedef) [edit] unsigned integer type returned by the sizeof operator
(typedef) [edit] returns an integer equal to the size of a range
(customization point object)[edit] returns a signed integer equal to the size of a range
(customization point object)[edit]

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