Golang fmt.Println can change the value of the array？

[LehmanHe]

$ go version
go version go1.13.5 darwin/amd64

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/helinming/Library/Caches/go-build"
GOENV="/Users/helinming/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/helinming/go/go1.13.5/bin"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/Users/helinming/go/go1.13.5"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/Users/helinming/go/go1.13.5/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/3_/n49czj355hddd0__5yzx3n200000gn/T/go-build181924234=/tmp/go-build -gno-record-gcc-switches -fno-common"

var x struct {
    a bool
    b int16
    c []int32
}

func main() {
    //a := []int32{1 << 9}
    //x.c = a
    pb := (*[]int8)(unsafe.Pointer(uintptr(unsafe.Pointer(&x)) + unsafe.Offsetof(x.c)))
    *pb = []int8{5}
    println(x.c[0])  // 5
    println(x.c[0])  // 5
    fmt.Println(x.c[0])  // 5
    fmt.Println(x.c[0])  // 327685 why????????
}

fmt.Println the same x.c[0] twice, but got different result. why?

[ianlancetaylor]

You are printing a []int8 as though it were a []int32. The results will depend on the contents of memory locations that you are not setting. Your code sets a single byte to 5, and then prints the contents of four bytes starting at that single byte. If the other other three bytes don't happen to contain 0, you will see values other than 5. It's certainly possible for the fmt package to change those bytes, since you didn't allocate them.

This is not a bug, so closing. If you want to ask questions about Go, please use a forum, not the issue tracker. See https://golang.org/wiki/Questions. Thanks.