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关于非常简单的程序的未定义参考

一旦我安装了Ubuntu 11.10,就会出现奇怪的错误.我想用我的C程序使用GD,所以我安装了包"libgd2-xpm-dev".一切都已安装 - 文件gd.h和libgd.a位于"/ usr/include"和"/ usr/lib"中.所以,我试图用GD编译简单的程序.

#include <stdio.h>
#include <gd.h>

int main()
{
        gdImagePtr im, im_clear;
        int black, white;
        FILE *out1;

        im = gdImageCreate(100, 100);
        im_clear = gdImageCreate(100, 100);

        white = gdImageColorAllocate(im, 255, 255, 255);
        black = gdImageColorAllocate(im, 0, 0, 0);
        return 0;
}

$ gcc -lgd gd.c
/tmp/cc6LReuX.o: In function `main':
gd2.c:(.text+0x19): undefined reference to `gdImageCreate'
gd2.c:(.text+0x31): undefined reference to `gdImageCreate'
gd2.c:(.text+0x59): undefined reference to `gdImageColorAllocate'
gd2.c:(.text+0x81): undefined reference to `gdImageColorAllocate'

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等等,什么？好的,我们来检查一下.