When using cgo to generate Go structs, some fields are ignored in the definition.

飞舟

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Jul 24, 2024, 7:29:39 AMJul 24

to golang-nuts

I have a C struct, and when I use cgo to generate Go structs, some fields are being ignored. I’m using go version go1.21.1 linux/amd64, and here is my env.

go env:

GO111MODULE='on'
GOARCH='amd64'
GOBIN=''
GOCACHE='/root/.cache/go-build'
GOENV='/root/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMODCACHE='/root/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/root/go'
GOPRIVATE=''
GOPROXY='https://goproxy.cn,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.21.1'
GCCGO='gccgo'
GOAMD64='v1'
AR='ar'
CC='gcc'
CXX='g++'
CGO_ENABLED='1'
GOMOD='/dev/null'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2970417006=/tmp/go-build -gno-record-gcc-switches'

and this is my C struct:

typedef struct PicHead
{
    unsigned short flag;
    unsigned char version[16];
    unsigned int headSize;
    int64_t fileSize;
    unsigned int macrograph;
    unsigned int personInfor;
    unsigned int hierarchy;
    unsigned int srcWidth;
    unsigned int srcHeight;
    unsigned int sliceWidth;
    unsigned int sliceHeight;
    unsigned int thumbnailWidth;
    unsigned int thumbnailHeight;
    unsigned char bpp;
    unsigned char quality;
    J_COLOR_SPACE colrSpace;
    float scale;
    double ruler;
    unsigned int rate;
    long long extraOffset;
    long long tileOffset;
     ImageFormat sliceFormat;
    unsigned char headSpace[48];
}PicHead;

this is cgo gen

type _Ctype_struct_PicHead struct {
    flag        _Ctype_ushort
    version     [16]_Ctype_uchar
    _       [40]byte
    bpp     _Ctype_uchar
    quality     _Ctype_uchar
    colrSpace   _Ctype_J_COLOR_SPACE
    scale       _Ctype_float
    _       [8]byte
    rate        _Ctype_uint
    extraOffset _Ctype_longlong
    tileOffset  _Ctype_longlong
    sliceFormat _Ctype_ImageFormat
    headSpace   [48]_Ctype_uchar
}

Message has been deleted

Ian Lance Taylor

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Jul 24, 2024, 8:32:34 AMJul 24

to 飞舟, golang-nuts

On Wed, Jul 24, 2024 at 5:29 AM 飞舟 <[email protected]> wrote:
>
> I have a C struct, and when I use cgo to generate Go structs, some fields are being ignored. I’m using go version go1.21.1 linux/amd64, and here is my env.

Please post code as plain text, rather than with a background. Plain
text is much easier to read. Thanks.

Also, please show us a complete, small, example. I tried your
example. I had to invent types for J_COLOR_SPACE and ImageFormat. It
worked fine.

Does your actual code use anything like #pragma packed? That will
cause this kind of problem, as Go does not currently have any way to
represent a packed struct.

Ian

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