Golang中的C语言函数执行顺序

Question

I am studying golang, but there is a part that I do not understand using c language.

In main, the c language function is executed for the second time, and the output is different depending on the IDE. Why does this print out?

package main

//#include<stdio.h>
//void callC() {
// printf("Calling C code!
");
//}
import "C"
import "fmt"


func main() {
    fmt.Println("A Go statement")
    C.callC()
    fmt.Println("Another Go statement")
}

-- in GoLand (Template: go build with Run after build option) --
output)
A Go statement
Another Go statement
Calling C code!

-- in terminal
$ go run hello.go
A Go statement
Calling C code!
Another Go statement

Answer 1

C's printf is implemented in libc, using lower level system calls. libc has buffers for I/O to improve performance, and it decides when to flush these buffers (specifically the stdout stream which printf emits to is buffered).

Go has its own printf using lower level system calls, it doesn't uses C's printf or libc at all for this. Therefore its flushing decisions are separate from C's printf.

So there's not problem here, really. printf doesn't guarantee unbuffered output (you can use the error stream for that, if necessary, of flush explicitly), so there is no guaranteed ordering between the C and Go versions.