将char数组从C传递到Go的通用函数

I am trying to copy content of structure in Go

type test struct {
    a string
    b string
}

to C structure.

typedef struct {
    char a[10];
    char b[75];
}test_c;

My requirement does not allow me to change the structure of member types of both Go and C. I have written the following code, to copy Go structure to C structure, and i am able to copy them too.

cmain.h

typedef struct {
    char a[10];
    char b[75];
}test_c;
void cmain(test_c* value);

cmain.c

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

void cmain(test_c *value) {
    printf("Inside C code
");
    printf("C code structure Member:a=%s
", value->a);
    printf("C code structure Member:b=%s
", value->b);
}

go_func.go

 package main
 import (
    /*
        #include "cmain.h"
    */
    "C"
    "fmt"
    "unsafe"
)

type test struct {
    a string
    b string
}

func main() {

    var p_go test
    var p_c C.test_c
    p_go.a = "ABCDEFGHIJ"
    p_go.b = "QRSTUVXWYZ"
    fmt.Println(unsafe.Sizeof(p_c.a))
    StructMemberCopy(&p_c.a, p_go.a)
    fmt.Println("In GO code
")
    fmt.Println("GO code structure Member:a=%s", p_go.a)
    fmt.Println("GO code structure Member:b=%s", p_go.b)

    fmt.Println("Call C function by passing GO structure
")
    C.cmain((*C.test_c)(unsafe.Pointer(&p_c)))

}

func StructMemberCopy(dest *[10]C.char, src string) {
    for i, _ := range src {
        dest[i] = C.char(src[i])
        fmt.Printf("%d %c 
", i, src[i])
    }
}

Here am trying to write a generalized function to copy the content of Go Structure member to C Structure

func StructMemberCopy(dest *[10]C.char, src string) {
        for i, _ := range src {
            dest[i] = C.char(src[i])
            fmt.Printf("%d %c 
", i, src[i])
        }
    }

In the above code, when i call the function StructMemberCopy(&p_c.a, p_go.a), with &p_c.a as argument the code compiles without any error, but when i send &p_c.b, it gives an error

cannot use &p_c.b (type *[75]C.char) as type *[10]C.char in argument to StructMemberCopy

Can anyone give some inputs as to how to write the generalized argument for func StructMemberCopy, as my C Structure array member size can vary. Mean it can become

typedef struct {
    char a[10];
    char b[75]; 
}test_c;

or typedef struct {
    char a[15];
    char b[40];
}test_c;