未定义对“ mpg123_open”的引用

Question

我正在测试mpg123库的功能，并且正在使用下面显示的代码。

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>
#include <cstring>
#include <mpg123.h>

#define INBUFF  16384
#define OUTBUFF 32768

void openfile(mpg123_handle* mh , char* filename){
    int             fnum;
    int             rbytes;
    int             mpg123Status = 0;
    int             channels = 0, encoding = 0;
    long            rate = 0;
    size_t          size;
    int             decodedbytes, decodestatus;
    int             fileSizeSamples;
    unsigned int    framesConsumed;
    unsigned char   *mp3InBuf, *mp3OutBuf;
    unsigned int    mp3InBufSize, mp3OutBufSize;
    size_t          decodedNow;

    mp3InBufSize    = 2048;
    mp3OutBufSize   = 32768;

    mp3InBuf        = new unsigned char[mp3InBufSize];
    mp3OutBuf       = new unsigned char[mp3InBufSize];

    //Open mp3 file for reading
    fnum = open(filename, O_RDONLY);
    if(fnum < 0){
        printf("ERROR opening file: %s\n", strerror(fnum));
        exit(0);
    }

    decodedbytes = 0;
    decodestatus = MPG123_NEED_MORE;

    mpg123Status = mpg123_init();
    if(mpg123Status){
        printf("Could not init MPG123: %d - %s\n", mpg123Status, mpg123_plain_strerror(mpg123Status));
        close(fnum);
        exit(0);
    }

    mh = mpg123_new(NULL, &mpg123Status);
    if(mh == NULL){
        printf("Could not open mpg123_handle: %d - %s\n", mpg123Status, mpg123_plain_strerror(mpg123Status));
        close(fnum);
        exit(0);
    }

    mpg123Status = mpg123_open_feed(mh);
    if (mpg123Status) {
        printf( "Could not open mpg123 feed: %d - %s\n",  mpg123Status, mpg123_plain_strerror(mpg123Status));
        close(fnum);
        exit(0);
    }

    mpg123_open(mh, filename);
    fileSizeSamples = MPG123_ERR;
    framesConsumed = 0;

    /* determine file parameters */
    mpg123Status = -1;
    printf("Start initial decode for file params.\n");
    while (MPG123_NEW_FORMAT!=mpg123Status) {
        /* file -> decoder */
        rbytes = read(fnum, mp3InBuf, mp3InBufSize);
        if (rbytes>0) {
            mpg123Status = mpg123_decode(mh, mp3InBuf, rbytes, mp3OutBuf, mp3OutBufSize, &size);
            if ((mpg123Status) && (MPG123_NEW_FORMAT!=mpg123Status)) {
                printf("Could not feed mpg123: read %d Bytes %d from file %d - %s\n",size, rbytes, mpg123Status, mpg123_plain_strerror(mpg123Status));
                close(fnum);
                exit(0);
            }
                mpg123_getformat(mh, &rate, &channels, &encoding);
        }
    }

    printf("MP3 at %d Hz %d channels %x encoding\n", rate, channels, encoding);

    /*Read entire file*/
    while(!EOF){
        rbytes = read(fnum,mp3InBuf,mp3InBufSize);
        decodestatus = mpg123_decode(   mh, mp3InBuf, mp3InBufSize,
                                        mp3OutBuf,mp3OutBufSize, &decodedNow);
        printf("%s",mp3OutBuf);
    }

    //Clean up
    close(fnum);
    mpg123_close(mh);
    mpg123_delete(mh);
    mpg123_exit();
    delete [] mp3InBuf;
    delete [] mp3OutBuf;
}

int main(int argc, char **argv) {
    mpg123_handle*  mh;

    //for(;;){
        for(int i=1; i<argc; i++){
            printf("Opening File: %s\n", argv[i]);
            openfile(mh, argv[i]);
            sleep(5);
        }
    //}
}

为了编译以上代码，我在linux中的命令中使用以下命令：

g++ -o mpg123example mpg123example.cpp -lmpg123 

我收到以下错误：

 In function `openfile(mpg123_handle_struct*, char*)':
mpg123example.cpp:(.text+0x196): undefined reference to `mpg123_open'
collect2: ld returned 1 exit status

我的困惑是，如果库无法正确链接，为什么不抱怨其他函数调用呢？ 任何建议，将不胜感激。

Answer 1

@zalman

# Makefile for mpg123example

# NOTES :
# $@ = target name
# $< = implicit source

PLATFORM=x86

# We assume to always build on an X86, so no cross compile for it

# We assume to always build on an X86, so no cross compile for it

# ARM Build Specifics
ifeq ($(PLATFORM), vs)
    CROSSCOMPILE=arm-none-linux-gnueabi-
    ROOTFS=/projects/armrfs/armel_dev02
    PLATFORMSTR="VS Exciter Board"
    CROSSLIBDIR=/projects/CodeSourcery/Sourcery_G++_Lite/arm-none-linux-gnueabi/libc
endif

# X86 Build Specifics
ifeq ($(PLATFORM), x86)
    CROSSCOMPILE=
    ROOTFS=
    PLATFORMSTR="Generic x86"
    CROSSLIBDIR=
endif

CFLAGS=-I $(ROOTFS)/usr/include/ -DPLATFORM=$(PLATFORM) -D_FILE_OFFSET_BITS=64
LDFLAGS=-L $(CROSSLIBDIR)/usr/lib/ -L $(ROOTFS)/usr/lib  -L $(ROOTFS)/usr/local/lib -lmpg123

CPP=$(CROSSCOMPILE)g++

CPPSRC= mpg123example.cpp

all: mpg123example

mpg123example: $(CPPSRC)
    $(CPP) -o mpg123example $(CFLAGS) $(LDFLAGS) mpg123example.cpp


clean: 
    rm -rf *.o mpg123example`