CGO Types
C作为一种混合编程语言已经很久了，无论那些广泛使用的包是用何种语言实现的，都导出了和C兼容的API。Go程序调用C程序，可以借助两种工具实现，一种是cgo，另一种是SWIG工具。Cgo是为C函数创建go绑定的工具；SWIG工具可以提供更复杂的特性来调用C++程序。（关于SWIG工具的使用，可以参考以前的《calling c++ from golang with swig 》系列随笔）。
本文主要讲述C语言类型、在CGO中可以引用的C类型及对应的引用类型名称。
查询C99标准文档（6.2.5 Types），主要类型包括：_Bool、char、signed char、unsigned char、short、unsigned short、int、unsigned int、long、unsigned long、long long、unsigned long long、float、double、long double、float _Complex、double _Complex、long double _Complex、void *、__int128_t、__uint128_t
在CGO中引用C类型的名称可以参考CGO官方文档（Command cgo）。Go references to C 部分给出了可以引用的数值类型名称。
综合两份参考文献，给出下面的类型列表。
|
C Types |
Cgo Types |
|
_Bool |
C._Bool |
|
char |
C.char |
|
signed char |
C.schar |
|
unsigned char |
C.uchar |
|
short |
C.short |
|
unsigned short |
C.ushort |
|
int |
C.int |
|
unsigned int |
C.uint |
|
long |
C.long |
|
unsigned long |
C.ulong |
|
long long |
C.longlong |
|
unsigned long long |
C.ulonglong |
|
float |
C.float |
|
double |
C.double |
|
long double |
不支持（unexpected: 16-byte float type - long double） |
|
float _Complex |
C.complexfloat |
|
double _Complex |
C.complexdouble |
|
long double _Complex |
不支持（ unexpected: 32-byte complex type - complex long double） |
|
void* |
unsafe.Pointer |
|
__int128_t |
[16]byte |
|
__uint128_t |
[16]byte |
C语言中的数值类型long double和long double _Complex在CGO中不能引用，编译报错。
写一个简单的程序来演示下：
package main
/*
#include <limits.h>
#include <float.h>
_Bool b = 1;
char c = 'A';
signed char sc = CHAR_MIN;
unsigned char usc = UCHAR_MAX;
short s = SHRT_MIN;
unsigned short us = USHRT_MAX;
int i = INT_MIN;
unsigned int ui = UINT_MAX;
long l = LONG_MIN;
unsigned long ul = ULONG_MAX;
long long ll = LONG_LONG_MIN;
unsigned long long ull = ULONG_LONG_MAX;
float f = FLT_MIN;
double d = DBL_MIN;
long double ld = LDBL_MIN;
float _Complex fc = 5+5i;
double _Complex dc = 5+5i;
long double _Complex ldc = 5+5i;
__int128_t i128 = 0;
__uint128_t ui128 = 3.4028236692093846346337460743177e+38;
void *ptr = 0;
*/
import "C"
import "fmt"
import "unsafe"
func main() {
fmt.Println(C.b)
fmt.Println(C.c)
fmt.Println(C.sc)
fmt.Println(C.usc)
fmt.Println(C.s)
fmt.Println(C.us)
fmt.Println(C.i)
fmt.Println(C.ui)
fmt.Println(C.l)
fmt.Println(C.ul)
fmt.Println(C.ll)
fmt.Println(C.ull)
fmt.Println(C.f)
fmt.Println(C.d)
//fmt.Println(C.ld)
fmt.Println(C.fc)
fmt.Println(C.dc)
//fmt.Println(C.ldc)
fmt.Println(C.i128)
fmt.Println(C.ui128)
fmt.Println(C.ptr)
fmt.Println("-------------------------------------------------")
fmt.Println(C._Bool(true))
fmt.Println(C.char('A'))
fmt.Println(C.schar(-128))
fmt.Println(C.uchar(255))
fmt.Println(C.short(C.SHRT_MIN))
fmt.Println(C.ushort(C.USHRT_MAX))
fmt.Println(C.int(C.INT_MIN))
fmt.Println(C.uint(C.UINT_MAX))
fmt.Println(C.long(C.LONG_MIN))
fmt.Println(C.ulong(C.ULONG_MAX))
fmt.Println(C.longlong(C.LONG_LONG_MIN))
fmt.Println(C.ulonglong(18446744073709551615))
fmt.Println(C.float(-1))
fmt.Println(C.double(-1))
//fmt.Println(C.longdouble(1))
fmt.Println(C.complexfloat(5 + 5i))
fmt.Println(C.complexdouble(5 + 5i))
C.i128 = [16]byte{15: 127}
fmt.Println(C.i128)
C.ui128 = [16]byte{15: 255}
fmt.Println(C.ui128)
C.ptr = unsafe.Pointer(nil)
fmt.Println(C.ptr)
}
运行后，输出结果如下：（运行环境：Windows 7 64位操作系统，go version go1.8.3 windows/amd64）
true 65 -128 255 -32768 65535 -2147483648 4294967295 -2147483648 4294967295 -9223372036854775808 18446744073709551615 1.1754944e-38 2.2250738585072014e-308 (5+5i) (5+5i) [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0] [255 255 255 255 255 255 255 255 255 255 255 255 255 255 255 255] <nil> ------------------------------------------------- true 65 -128 255 -32768 65535 -2147483648 4294967295 -2147483648 4294967295 -9223372036854775808 18446744073709551615 -1 -1 (5+5i) (5+5i) [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 127] [0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 255] <nil>