What is the size of float and double in C and C++?

The sizes of float and double in C and C++ depend on the system architecture and compiler implementation. However, most modern systems adhere to the IEEE 754 standard for floating-point representation, which defines the sizes and precision.

Default Sizes

C (Standard: C89/C99/C11)

C++ (Standard: C++98/C++11/C++17/C++20)

Explanation

1. float:
   • Uses 4 bytes (32 bits).
   • Precision: About 6-7 significant decimal digits.
   • Range: Approximately ±3.4 × 10^38.
2. double:
   • Uses 8 bytes (64 bits).
   • Precision: About 15-16 significant decimal digits.
   • Range: Approximately ±1.7 × 10^308.
3. long double:
   • The size of long double varies depending on the compiler and platform:
     • On most modern systems: 8 bytes (same as double).
     • On x86 extended precision: 10 bytes (80 bits).
     • On some systems (e.g., GCC on Linux): 16 bytes (128 bits).

Platform-Specific Variations

32-bit vs. 64-bit Systems

• The sizes of float and double typically remain the same (4 bytes and 8 bytes, respectively), regardless of whether the system is 32-bit or 64-bit.

Compiler Differences

• Some compilers may provide options or extensions that alter the size of long double but not float or double.

How to Determine Sizes Programmatically

You can use the sizeof operator to determine the size of these types on your specific system:

C Code Example

#include <stdio.h>

int main() {
    printf("Size of float: %zu bytes\n", sizeof(float));
    printf("Size of double: %zu bytes\n", sizeof(double));
    printf("Size of long double: %zu bytes\n", sizeof(long double));
    return 0;
}

C++ Code Example

#include <iostream>

int main() {
    std::cout << "Size of float: " << sizeof(float) << " bytes" << std::endl;
    std::cout << "Size of double: " << sizeof(double) << " bytes" << std::endl;
    std::cout << "Size of long double: " << sizeof(long double) << " bytes" << std::endl;
    return 0;
}

Summary

• float: 4 bytes, ~6-7 digits precision.
• double: 8 bytes, ~15-16 digits precision.
• long double: Typically 8, 10, or 16 bytes depending on the platform.

Let me know if you’d like further clarification or assistance!