MPFR：未定义参考| 安装不正确？

我正在尝试在Ubuntu 20.04上使用mpfr库。

我已经安装了：

sudo apt-get install -y libmpfr-dev libmpfr6

我有一个简单的测试代码（从某处的教程复制）：

#include <iostream>
#include <mpfr.h>

int main() {
    mpfr_t s, t;
    mpfr_init2(s, 2000);
    mpfr_set_d(s, 22, MPFR_RNDD);
    mpfr_init2(t, 2000);
    mpfr_set_d(t, 7, MPFR_RNDD);
    mpfr_div(s, s, t, MPFR_RNDD);
    mpfr_out_str(stdout, 10, 0, s, MPFR_RNDD);
    std::cout << std::endl;
    mpfr_clear(s);
    mpfr_clear(t);
    mpfr_free_cache();
}

它看起来像是C代码，但这只是一个玩具示例。在实际程序中，它将是一个C++代码，因此我使用cpp扩展和g++编译器。

我用它编译：

g++ -O0 -Wall --std=c++14 -L/usr/lib -lmpfr -lgmp -o test test.cpp

而且我收到错误消息，好像缺少库定义文件...

/usr/bin/ld: /tmp/cc1XbFhH.o: in function `main':
test.cpp:(.text+0x28): undefined reference to `mpfr_init2'
/usr/bin/ld: test.cpp:(.text+0x45): undefined reference to `mpfr_set_d'
/usr/bin/ld: test.cpp:(.text+0x56): undefined reference to `mpfr_init2'
/usr/bin/ld: test.cpp:(.text+0x73): undefined reference to `mpfr_set_d'
/usr/bin/ld: test.cpp:(.text+0x8c): undefined reference to `mpfr_div'
/usr/bin/ld: test.cpp:(.text+0xb2): undefined reference to `__gmpfr_out_str'
/usr/bin/ld: test.cpp:(.text+0xd4): undefined reference to `mpfr_clear'
/usr/bin/ld: test.cpp:(.text+0xe0): undefined reference to `mpfr_clear'
/usr/bin/ld: test.cpp:(.text+0xe5): undefined reference to `mpfr_free_cache'
collect2: error: ld returned 1 exit status

我做错了吗？我知道图书馆是有：

$ dpkg -L libmpfr6
/.
/usr
/usr/lib
/usr/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu/libmpfr.so.6.0.2
/usr/share
/usr/share/doc
/usr/share/doc/libmpfr6
/usr/share/doc/libmpfr6/AUTHORS
/usr/share/doc/libmpfr6/BUGS
/usr/share/doc/libmpfr6/NEWS.gz
/usr/share/doc/libmpfr6/README
/usr/share/doc/libmpfr6/TODO.gz
/usr/share/doc/libmpfr6/changelog.Debian.gz
/usr/share/doc/libmpfr6/copyright
/usr/lib/x86_64-linux-gnu/libmpfr.so.6

$ dpkg -L libmpfr-dev
/.
/usr
/usr/include
/usr/include/mpf2mpfr.h
/usr/include/mpfr.h
/usr/lib
/usr/lib/x86_64-linux-gnu
/usr/lib/x86_64-linux-gnu/libmpfr.a
/usr/lib/x86_64-linux-gnu/pkgconfig
/usr/lib/x86_64-linux-gnu/pkgconfig/mpfr.pc
/usr/share
/usr/share/doc
/usr/share/doc/libmpfr-dev
/usr/share/doc/libmpfr-dev/copyright
/usr/lib/x86_64-linux-gnu/libmpfr.so
/usr/share/doc/libmpfr-dev/AUTHORS
/usr/share/doc/libmpfr-dev/BUGS
/usr/share/doc/libmpfr-dev/NEWS.gz
/usr/share/doc/libmpfr-dev/README
/usr/share/doc/libmpfr-dev/TODO.gz
/usr/share/doc/libmpfr-dev/changelog.Debian.gz
/usr/share/doc/libmpfr-dev/changelog.gz