How to use sizeof in c++

The sizeof operator in C returns the number of bytes occupied by the specified data type or variable. It can be used to determine memory size, perform memory management, align data structures, and determine function pointer size. For example, sizeof(int) returns the number of bytes occupied by an integer, while sizeof(a) returns the number of bytes occupied by the variable a. Note that the value returned by sizeof varies between compilers and platforms, and for pointer types it returns the size of the pointer's introspection, not the size of the object it points to.

Usage of sizeof in C

What is sizeof?

sizeof is an operator in C that returns the number of bytes occupied by a specified data type or variable.

Syntax:

sizeof(type)  // 返回数据类型所需的字节数
sizeof(variable)  // 返回变量所需的字节数

Use example:

• Determine the memory size of a variable or data type: By passing variables or data types as arguments, you can determine the amount of memory they require.
• Memory Management: When allocating or freeing memory, sizeof can help determine the required size.
• Data structure alignment: Some data structures require specific byte alignment. sizeof can be used to determine the amount of alignment required.
• Function pointer size: sizeof can be used to determine the required size of a function pointer.

Example:

int main() {
  int a = 10;
  float b = 3.14;

  // 输出 a 和 b 所占用的字节数
  std::cout << "int a occupies " << sizeof(a) << " bytes" << std::endl;
  std::cout << "float b occupies " << sizeof(b) << " bytes" << std::endl;
  
  return 0;
}

Output:

<code>int a occupies 4 bytes
float b occupies 4 bytes</code>

Note:

• sizeof returns a compiler-specific value that may vary between compilers and platforms.
• For pointer types, sizeof returns the size of the pointer itself (usually 4 or 8 bytes), not the size of the object pointed to.
• For arrays, sizeof returns the total number of bytes of elements in the array, not the size of individual elements.

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