Examples of calling C code from Golang

cgo1.go

package main

//#include<stdio.h>
//void inC() {
//    printf("I am in C code now!\n");
//}
import "C"
import "fmt"

func main() {
    fmt.Println("I am in Go code now!")
    C.inC()
}

cgo2.c

#include<stdio.h>

void inCFile() {
    printf("I am in C code in a .c file now!\n");
}

cgo2.go

package main

/*
extern void inCFile();
*/
import "C"
import "fmt"

func main() {
    fmt.Println("I am in Go code now!")
    C.inCFile()
}

cgo3.c

#include<stdio.h>
#include "_cgo_export.h"

void inCFile() {
    printf("I am in C code in a .c file now!\n");
    callFromC();
}

cgo3.go

package main

/*
#include<stdio.h>
extern void inCFile();
*/
import "C"
import "fmt"

func main() {
    fmt.Println("I am in Go code now!")
    C.inCFile()
}

//export callFromC
func callFromC() {
    fmt.Println("I am in Go code but I was called from C!")
}

cstring1.c

#include<stdio.h>
#include "_cgo_export.h"

char * inCFile(char *str) {
    char *ret = "C String";
    printf("Received string from Go: %s\n", str);
    return ret;
}

cstring1.go

package main

/*
#include<stdio.h>
#include <stdlib.h>
extern char * inCFile(char *str);
*/
import "C"
import (
    "fmt"
    "unsafe"
)

func main() {
    cstr := C.CString("Go string!")
    defer C.free(unsafe.Pointer(cstr))
    cString := C.inCFile(cstr)
    gostr := C.GoString(cString)
    fmt.Println("Received string from C: " + gostr)
}