Using the C language code instance in Golang

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Using the C language code instance in Golang

Submission: Junjie font: [Increase listening decrease] Type: Reprint time: 2014-10-27 Listen, I want to comment.

This article mainly introduces the use of C language code examples in Golang, this article first gives a Hello World example, Golang reference C example, and summarizes some of the areas to note, the need for friends can refer to the following

CGO makes it possible to use C code in Golang.

Hello World

To have a more intuitive understanding, let's look at a simple example of creating a file Main.go:

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Package Main
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/*
#include <stdio.h>
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void Sayhi () {
Listen and listen to printf ("Hi");
}
*/
Import "C"
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Func Main () {
Listen and listen to C.sayhi ()
}

Execute the program:

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Go Run main.go

The program executes and outputs hi (more examples can be seen $GOROOT/misc/cgo).

Preparations under Windows

If you want to use CGO on Windows, then you need to install the GCC compiler, here I use MINGW-W64.

Set compilation and link flags

We imported a pseudo package (Pseudo-package) using the import "C", which we used to use C code. Before import "C", comments that follow the import "C" can include:

1. Compiler and linker flags
2.C Code

We can set compiler and linker flags by #cgo directives, for example:

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#cgo CFLAGS:-dpng_debug=1
#cgo AMD64 386 CFLAGS:-dx86=1
#cgo Ldflags:-lpng
#include <png.h>
Import "C"

Incidentally, these directives can contain build constraints (build constraint), as detailed in the following: http://golang.org/pkg/go/build/#hdr-build_constraints.

The commonly used #cgo directives are:

The 1.CPPFLAGS, CFLAGS instruction is used to compile the C file in the current package (any. C,. S,. S file)
The 2.CPPFLAGS, cxxflags instruction is used to compile C + + files in the current package (any. cpp,. cc,. cxx files)
The 3.LDFLAGS directive is used to specify linker flags
The 4.pkg-config directive is used to obtain compiler and linker flags through the Pkg-config tool (for example: #cgo pkg-config:png Cairo)

Golang Reference C

Points to note on the structure:

1.C struct domain name if the keyword is Golang, the access needs to precede the domain name with _. For example, there is a struct variable x in C, and there is a field type in the struct that corresponds to this variable, so you need to access the Type field through X._type in Golang.
2. A struct's bit field, non-aligned data, and so on cannot be ignored when represented in Golang
A domain of type C cannot be used in a 3.Golang struct

The standard C numeric type corresponds to:

1.c.char
2.c.schar (signed Char)
3.c.uchar (unsigned char)
4.c.short
5.c.ushort (unsigned short)
6.c.int
7.c.uint (unsigned int)
8.c.long
9.c.ulong (unsigned long)
10.c.longlong (Long Long)
11.c.ulonglong (unsigned long Long)
12.c.float
13.c.double

Any C function (including void functions) can return a return value and C's errno variable (as an error):

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N, Err: = C.sqrt (-1)
_, Err: = C.voidfunc ()

A direct call to a C function pointer is not currently supported.

There are special functions that can be used to convert between C and Golang types (by means of data copies), pseudo-defined as follows:

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Golang string to C string
The string for C is allocated using malloc, so the caller of this function
Need to call C.free to free memory
Func c.cstring (String) *c.char
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Convert C string to Golang string
Func c.gostring (*c.char) string
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Converts a certain length of C string to a Golang string
Func c.gostringn (*c.char, C.int) string
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Convert a chunk of C memory into a byte array of Golang
Func c.gobytes (unsafe. Pointer, c.int) []byte

Other points to note:

The void* in the 1.C language corresponds to unsafe. Pointer
The structure, Union, enumeration type (not the variable) in the 2.C language requires struct_, union_, enum_ prefix access in the Golang. Because the data type is not federated in Golang, the union of C is represented as a byte array in Golang
3. Those types that are equivalent to the C language are not exportable