调用共享库的cgo:找不到库或函数？

我正在使用Go编程语言第13章的示例代码，如下所示：

$ cat bzip2.c
#include <bzlib.h>

int bz2compress(bz_stream *s, int action,
                char *in, unsigned *inlen, char *out, unsigned *outlen) {
    s->next_in = in;
    s->avail_in = *inlen;
    s->next_out = out;
    s->avail_out = *outlen;
    int r = BZ2_bzCompress(s, action);
    *inlen -= s->avail_in;
    *outlen -= s->avail_out;
    s->next_in = s->next_out = NULL;
    return r;
}

$ cat usebzip2.go
// Package bzip provides a writer that uses bzip2 compression (bzip.org).
package main
import "C"

import (
    "io"
    "log"
    "os"
    "testing"
    "unsafe"
)

type writer struct {
    w      io.Writer // underlying output stream
    stream *C.bz_stream
    outbuf [64 * 1024]byte
}

// Close flushes the compressed data and closes the stream.
// It does not close the underlying io.Writer.
func (w *writer) Close() error {
    if w.stream == nil {
        panic("closed")
    }
    defer func() {
        C.BZ2_bzCompressEnd(w.stream)
        C.bz2free(w.stream)
        w.stream = nil
    }()
    for {
        inlen, outlen := C.uint(0), C.uint(cap(w.outbuf))
        r := C.bz2compress(w.stream, C.BZ_FINISH, nil, &inlen,
            (*C.char)(unsafe.Pointer(&w.outbuf)), &outlen)
        if _, err := w.w.Write(w.outbuf[:outlen]); err != nil {
            return err
        }
        if r == C.BZ_STREAM_END {
            return nil
        }
    }
}

// NewWriter returns a writer for bzip2-compressed streams.
func NewWriter(out io.Writer) io.WriteCloser {
    const blockSize = 9
    const verbosity = 0
    const workFactor = 30
    w := &writer{w: out, stream: C.bz2alloc()}
    C.BZ2_bzCompressInit(w.stream, blockSize, verbosity, workFactor)
    return w
}

func main() {
    w := NewWriter(os.Stdout)
    if _, err := io.Copy(w, os.Stdin); err != nil {
        log.Fatalf("bzipper: %v\n", err)
    }
    if err := w.Close(); err != nil {
        log.Fatalf("bzipper: close: %v\n", err)
    }
}

linux环境LD_LIBRARY_路径包含，然后go build失败：

go build usebzip2.go
# command-line-arguments
/tmp/go-build677611698/b001/_x002.o: In function `_cgo_22d5d7fabfe4_Cfunc_bz2compress':
/tmp/go-build/cgo-gcc-prolog:118: undefined reference to `bz2compress'
collect2: error: ld returned 1 exit status

那么如何修复它呢？我使用的是Ubuntu18.04LTS。非常感谢

不要运行：

go build usebzip2.go

而是：

go build

您不需要在bzip2.c上直接调用gcc。当您使用此过程时，您将收到更多但不同的错误，因为您没有在以下命令之前输入正确的指令：

import "C"

线路。您需要一条注释或一系列注释，告诉cgo您打算提供的函数，或者内联提供这些函数，并指导链接阶段使用-lbz2。特别是，您需要：

包括 提供bz2alloc函数 提供一个bz2free函数 为bz2compress函数提供声明 将LDFLAGS设置为包含-lbz2 实际的bz2alloc和bz2free都很短且简单，因此可以直接包含在此标题块中：

package main

/*
#cgo LDFLAGS: -lbz2     
#include <bzlib.h>
#include <stdlib.h>
bz_stream *bz2alloc() { return calloc(1, sizeof(bz_stream)); }
int bz2compress(bz_stream *s, int action,
    char *in, unsigned *intlen, char *out, unsigned *outlen);
void bz2free(bz_stream* s) { free(s); }
*/      
import "C"

这当然是因为类型编写器没有实现Write

有练习13.3的完整版本，但不是我的。请注意，它们还扩展了它们的功能以使用锁定，从而可以安全地同时从多个goroutine调用write函数

package main

/*
#cgo LDFLAGS: -lbz2     
#include <bzlib.h>
#include <stdlib.h>
bz_stream *bz2alloc() { return calloc(1, sizeof(bz_stream)); }
int bz2compress(bz_stream *s, int action,
    char *in, unsigned *intlen, char *out, unsigned *outlen);
void bz2free(bz_stream* s) { free(s); }
*/      
import "C"

./usebzip2.go:60:2: cannot use w (type *writer) as type io.WriteCloser in return argument:
        *writer does not implement io.WriteCloser (missing Write method)