Go-C conversion
- Go course
- Advanced
- Lesson 16/68
- 4 min
Learn conversion between Go string and C.CString.
String conversion
Go strings carry their length, while C strings end with \0. C.CString(s) copies a Go string into C memory; C.GoString(p) turns a *C.char into a Go string.
cs := C.CString("merhaba")
defer C.free(unsafe.Pointer(cs))
fmt.Println(C.strlen(cs)) // 7Byte slices
For byte data, C.CBytes(b) copies a []byte into C memory and C.GoBytes(p, n) copies n bytes from C memory into a Go slice. All these conversions copy; with large data their cost matters.
Practice String length
Add #include <stdlib.h> and #include <string.h> in the preamble. Create a C.CString for "gopher", free it with defer C.free(unsafe.Pointer(cs)) and print C.strlen(cs).
Starter code
package main
/*
// C kodu buraya
*/
import "C"
import (
"fmt"
"unsafe"
)
func main() {
// buraya yaz
}Sample solution
package main
/*
#include <stdlib.h>
#include <string.h>
*/
import "C"
import (
"fmt"
"unsafe"
)
func main() {
cs := C.CString("gopher")
defer C.free(unsafe.Pointer(cs))
fmt.Println(C.strlen(cs))
}Expected output
6
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 Who frees the memory allocated by <code>C.CString</code>?
- You, with C.free Correct answer
- The Go garbage collector
- It is freed automatically on exit only
- The C.GoString call
Explanation: C.CString allocates C memory with malloc; the GC can't see it, so it leaks unless freed with C.free.
2 Convert a C string to Go
p := C.CString("go")
s := C.____(p)p := C.CString("go")
s := C.GoString(p)Explanation: C.GoString copies a *C.char into a Go string.
3 Conversion functions
| Term | Meaning |
|---|---|
C.CString |
Go → C string |
C.GoString |
C → Go string |
C.CBytes |
Go → C bytes |
C.GoBytes |
C → Go bytes |