Get sizeof internal go struct

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05-10-2024

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Unmasking the Size of Internal Go Structs: A Deep Dive

Go's elegant syntax and powerful features often leave developers wondering about the underlying implementation details, especially when it comes to data structures. One such curiosity arises when dealing with structs: how do we determine the size of a struct in memory?

The Puzzle:

Let's say we have a simple Go struct like this:

type MyStruct struct {
    Name string
    Age  int
}

While we know Name is a string and Age is an integer, we don't know how much space they occupy in memory when combined within the MyStruct. Can we simply add the individual sizes of string and int to get the total size of MyStruct?

The Solution:

Unfortunately, it's not that straightforward. Go's internal representation of structs involves some behind-the-scenes magic. Here's why:

1. Memory Alignment: To optimize performance, Go aligns data types on specific memory boundaries. This means the struct's fields are arranged in a way that minimizes memory access time.
2. Hidden Fields: Structs, under the hood, might have additional hidden fields for internal bookkeeping, such as pointers to type information.

The Unsolved Mystery:

You cannot directly determine the size of a struct in Go using standard built-in functions like sizeof. This is because Go's runtime dynamically manages memory allocation and hides the internal representation of structs from the developer.

Unveiling the Secret:

While we can't directly measure the size, we can use some clever techniques to gain insights:

• Reflection: The reflect package offers a way to examine the underlying structure of Go types. We can use the Sizeof function to calculate the memory size of a struct's underlying data representation:

  package main
  
  import (
      "fmt"
      "reflect"
  )
  
  type MyStruct struct {
      Name string
      Age  int
  }
  
  func main() {
      s := MyStruct{}
      size := reflect.TypeOf(s).Size()
      fmt.Println("Size of MyStruct:", size)
  }
  

  This approach doesn't provide the exact memory footprint of the struct due to hidden fields.

• Unsafe Package: The unsafe package, with its caveat of being potentially dangerous, provides a way to access raw memory addresses. We can utilize the Sizeof function to get the size of a struct:

  package main
  
  import (
      "fmt"
      "unsafe"
  )
  
  type MyStruct struct {
      Name string
      Age  int
  }
  
  func main() {
      size := unsafe.Sizeof(MyStruct{})
      fmt.Println("Size of MyStruct:", size)
  }
  

  However, using unsafe package should be reserved for advanced scenarios where you have a deep understanding of memory management and the risks involved.

Important Considerations:

• The size of a struct can vary based on the Go version and platform.
• Struct sizes can be influenced by factors like garbage collection and pointer alignment.
• The actual size in memory may be greater due to padding and overhead associated with internal struct management.

Conclusion:

While we can't directly determine the exact size of a Go struct in bytes, techniques like reflection and the unsafe package offer insights into the memory footprint of its underlying data representation. Understanding these limitations and utilizing appropriate techniques is crucial for efficient memory management and optimizing performance in your Go applications.