c - Why cgo's performance is so slow? is there something wrong with my testing code?

Question

I'm doing a test: compare excecution times of cgo and pure Go functions run 100 million times each. The cgo function takes longer time compared to the Golang function, and I am confused with this result. My testing code is:

package main

import (
    "fmt"
    "time"
)

/*
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

void show() {

}

*/
// #cgo LDFLAGS: -lstdc++
import "C"

//import "fmt"

func show() {

}

func main() {
    now := time.Now()
    for i := 0; i < 100000000; i = i + 1 {
        C.show()
    }
    end_time := time.Now()

    var dur_time time.Duration = end_time.Sub(now)
    var elapsed_min float64 = dur_time.Minutes()
    var elapsed_sec float64 = dur_time.Seconds()
    var elapsed_nano int64 = dur_time.Nanoseconds()
    fmt.Printf("cgo show function elasped %f minutes or 
elapsed %f seconds or 
elapsed %d nanoseconds
",
        elapsed_min, elapsed_sec, elapsed_nano)

    now = time.Now()
    for i := 0; i < 100000000; i = i + 1 {
        show()
    }
    end_time = time.Now()

    dur_time = end_time.Sub(now)
    elapsed_min = dur_time.Minutes()
    elapsed_sec = dur_time.Seconds()
    elapsed_nano = dur_time.Nanoseconds()
    fmt.Printf("go show function elasped %f minutes or 
elapsed %f seconds or 
elapsed %d nanoseconds
",
        elapsed_min, elapsed_sec, elapsed_nano)

    var input string
    fmt.Scanln(&input)
}

and result is:

cgo show function elasped 0.368096 minutes or 
elapsed 22.085756 seconds or 
elapsed 22085755775 nanoseconds

go show function elasped 0.000654 minutes or 
elapsed 0.039257 seconds or 
elapsed 39257120 nanoseconds

The results show that invoking the C function is slower than the Go function. Is there something wrong with my testing code?

My system is : mac OS X 10.9.4 (13E28)

Answer 1

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