big.Int not equal to one received after big.setBytes(bigint.Bytes())

Question

I want to convert a big int to bytes and the bytes back to big int and then compare the two values. I am doing it using similar code as below:

package main

import "fmt"
import "math/big"

func main() {
    input := "37107287533902102798797998220837590246510135740250"
    a := big.NewInt(0)
    a.SetString(input, 10)
    fmt.Println("number =", a)

    z := a.Bytes()
    b := big.NewInt(0)
    b.SetBytes(z)

    fmt.Println("number =", b)

    if a!=b{
        fmt.Println("foo")
    }

}

The output is:

number = 37107287533902102798797998220837590246510135740250
number = 37107287533902102798797998220837590246510135740250
foo

This is strange, the numbers look equal. The code inside if loop should not be executed. What am I missing here?

Answer 1

You are comparing the pointers to the big.Int values, and not the internal big.Int values. Comparing big.Int values must be done using the Int.Cmp method:

func (x *Int) Cmp(y *Int) (r int)

Cmp compares x and y and returns:

-1 if x <  y
0 if x == y
+1 if x >  y

if a.Cmp(b) != 0 {
    fmt.Println("foo")
}