How to see how much memory occupies such a variable in C ++? And how do you define it?

I made an example in C ++ standards showing the size of the variables as you requested. Note that sizeof is an operator, it does not even need parentheses in some situations. This operator takes the data size used as operand, in this case the variable, at compile time, so it has no cost at runtime.

In general in C ++ do not use legacy C libraries.

#include <iostream>
#define tamanho 10
const int elementos = 10;
using namespace std;

int main() {
    int a = 1;
    char b = 'a';
    float c = 1.0f;
    double d = 2.0d;
    short e = 1000;
    long f = 100000;
    int *g = new int[tamanho];
    int h[elementos];
    cout << "a tem " << sizeof(a) << " bytes\n";
    cout << "b tem " << sizeof(b) << " bytes\n";
    cout << "c tem " << sizeof(c) << " bytes\n";
    cout << "d tem " << sizeof(d) << " bytes\n";
    cout << "e tem " << sizeof(e) << " bytes\n";
    cout << "f tem " << sizeof(f) << " bytes\n";
    cout << "g tem " << sizeof(g) << " bytes\n"; //provavelmente não é o resultado esperado
    cout << "h tem " << sizeof(h) << " bytes\n";
    return 0;
}

See running on ideone .

Note that allocating data dynamically can lead to problems determining the size of the allocation. You would have to have other ways of figuring out the allocated size. But also note that in this case the size of the variable really is the size of the pointer. The result is not wrong. The variable itself occupies 4 bytes in 32-bit architectures. What the pointer points to is that it will have another extra size, it shows in the variable h (static allocation) that was not allocated with a pointer as it was in g (dynamic allocation).

Learn more about the difference in stack and heap .

the define works like this:

#define TAMMAX 100

first comes the next defines the name and what it contains in that name, when and compiled everything that is named TAMMAX in your code and replaced with 100, for example:

int vetor[TAMMAX] // vetor de 100 indices

You can find out how many bytes a variable occupies through the sizeof() function.

This function takes a variable as an argument, or reserved words that represent the variables: char, int, float, etc.

Example:

printf("Char: %d bytes\n", sizeof(char));
printf("Int: %d bytes\n", sizeof(int));
printf("Float: %d bytes\n", sizeof(float));
printf("Double: %d bytes\n", sizeof(double));

Do not forget to include the stdio.h

  

Font

To use the define is very simple:

#define CONTADOR 0

Then just use the name of define in the code.

Example:

#define CONTADOR 10
int main() {
  int vetor[CONTADOR]; //Vetor com CONTADOR posições
}