C data types

Learn types like C.int and C.char.

C data types

C types appear in Go with names like C.int, C.long, C.double, C.char. They are not the same as Go's int or float64; an explicit conversion is required.

var a C.int = 5
b := int(a) * 2      // C.int → int
c := C.double(1.5)   // float64 → C.double

Sizes can vary by platform: C.long is 8 bytes on Linux and 4 on Windows.

Structs and enums

A C struct nokta is used in Go as C.struct_nokta; you access its fields directly. enum constants also come through as C.NAME.

/*
struct nokta { int x; int y; };
*/
import "C"

var p C.struct_nokta
p.x = 3

Exercise Type conversion

In the preamble define double yarim(double x) { return x / 2; }. Convert v := 9.0 to C.double, pass it to the function, convert the result to float64 and print it.

Show example solution

package main

/*
double yarim(double x) { return x / 2; }
*/
import "C"

import "fmt"

func main() {
    v := 9.0
    r := float64(C.yarim(C.double(v)))
    fmt.Println(r)
}

Test yourself

If a C function returns <code>double</code>, how do you get a <code>float64</code> in Go?
- C.float64(C.f())
- float64(C.f())
- C.f().(float64)
- No conversion is needed
Show answer

float64(C.f()) — C.double is a separate type; to use it in Go you convert it explicitly with float64(...).

Convert to a C type

x := 10
r := C.kare(C.____(x))

Show answer

x := 10
r := C.kare(C.int(x))

C and Go types

C.int

int32 sized
C.double

float64 counterpart
C.char

One byte
C.struct_nokta

A C struct

Next lesson: Go-C conversion

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