C ++ type byte size of each test

Basic data type declaration

I respective basic types of PC data sizes are as follows:

Code:

#include <iostream>

using namespace std;

int main() {
    cout << "char: " << sizeof(char) << endl;   // 1
    cout << "bool: " << sizeof(bool) << endl;   // 1
    cout << "int: " << sizeof(int) << endl;    // 4
    cout << "long: " << sizeof(long) << endl;   // 4
    cout << "long long: " << sizeof(long long ) << endl; // 8
    cout << "float: " << sizeof(float) << endl;  // 4
    cout << "double: " << sizeof(double) << endl; // 8
    return 0;
}

Out:

char: 1
bool: 1
int: 4
long: 4
long long: 8
float: 4
double: 8

Structure

Code:

#include <iostream>

using namespace std;

struct A {
    bool one;
};

struct B {
    int one;    // 4
    bool two;   // 1
};

struct C {
    bool one;   // 1
    int two;    // 4
    double three;   // 8
};

struct D {
    char one[10]; // 12
    double two;   // 8
    double three; // 8
};


int main()
{
    cout << "A: " << sizeof(A) << endl;
    cout << "B: " << sizeof(B) << endl;
    cout << "C: " << sizeof(C) << endl;
    cout << "D: " << sizeof(D) << endl;
}

Out:

A: 1
B: 8
C: 16
D: 32

Add compiler directives head:

#pragma pack(4)

Out:

A: 1
B: 8
C: 16
D: 28

Memory Alignment: In order to facilitate the reading of the CPU, the data structure of the compiler will be a fixed integer multiple of alignment, and this number is usually fixed with 4 bytes and 8 bytes. Generally determines the word length factor is a CPU, i.e. 32bit word length, for the CPU will read 4 bytes, to be more quickly and easily than the 1-byte read. And replaced 64bit word length of the CPU, wanted to 8-byte read will be more quickly and easily.

In the compiler-specific platforms, generally have a default "Align coefficient" (also called modulus aligned), i.e., does not correspond to the current CPU alignment word length coefficients. This factor can be changed by a pre-compiled command #pragma pack (n), where n is and you have to specify the "alignment factor."

Thus, I use the compiler MinGW-W64 gcc version 8.1.0aligned coefficients default is 8 bytes, i.e. corresponding to the 64bit CPU.