How to Integrate Go Functions into Existing C Projects Using GCCGO?

Using Go Within Existing C Projects

Background:
You have a C program comprised of multiple object files stored in an archive file (.a). You intend to add a new Go file to the project, compile it into an object file, and incorporate it into the existing archive.

Objective:
Integrate Go functions into your C program.

Process:

1. Compile the Go File into an Object File:

• Run the following command:

  gccgo -c printString.go -o printString.o -fgo-prefix=print -Wall -Werror -march=native

2. Call Go Functions from C:

• In your c_caller.c file, declare an extern function:

  extern int PrintString(char*) __asm__ ("print.main.PrintString");

• In the main function, call the Go function and handle the result:

  int result = PrintString(string_to_pass);
  if (result) { printf("Everything went as expected!\n"); }
  else       { printf("Uh oh, something went wrong!\n"); }

3. Using GCCGO to Build the Entire Project:

• Run the following command:

  gccgo -o main c_caller.c printString.o -Wall -Werror -march=native

4. Addressing Errors:

• If you encounter errors like "undefined reference to main.main", ensure that you have a main function in your C code.
• If you encounter errors like "cannot find -lgo," verify that the LD_LIBRARY_PATH environment variable is set to point to the folder where libgo.so is located.

Alternative Solution in Go 1.5:

In Go 1.5 (coming in August), a new feature enables the creation of C-compatible libraries from Go code. With this feature, you can build a static or shared library directly from a Go file, eliminating the need for intermediate object files.

Example:

• In main.c:

  #include <stdio.h>
  
  int main()
  {
    char *string_to_pass = NULL;
    if (asprintf(&amp;string_to_pass, "This is a test.") < 0) {
        printf("asprintf fail");
        return -1;
    }
  
    PrintString(string_to_pass);
    return 0;
  }

• In main.go (compiled with go build -buildmode c-archive ... for static or go build -buildmode c-shared ... for shared library):

  package main
  
  import "C"
  import "fmt"
  
  //export PrintString
  func PrintString(cs *C.char) {
    s := C.GoString(cs)
    fmt.Println(s)
  }
  
  func main() {}

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