C语言 ld：未定义对符号“log2@@GLIBC_2.2.5”的引用
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ld: undefined reference to symbol 'log2@@GLIBC_2.2.5'
提问by Jiew Meng
Whats wrong with
怎么了
for (level = 1; level <= log2((double)size); level++)
^
Seems like its from using log2()but whats wrong? I am using it with OpenMPI code actually, but commenting this line fixes things.
似乎它从使用log2()但有什么问题？我实际上将它与 OpenMPI 代码一起使用，但注释这一行可以解决问题。
Full Source(http://pastie.org/7559178)see line 40
完整来源( http://pastie.org/7559178)见第 40 行
[jiewmeng@JM Assign3]$ mpicc -o cpi cpi.c && mpirun -np 16 cpi
/usr/bin/ld: /tmp/cca9x4he.o: undefined reference to symbol 'log2@@GLIBC_2.2.5'
/usr/bin/ld: note: 'log2@@GLIBC_2.2.5' is defined in DSO /usr/lib/libm.so.6 so try adding it to the linker command line
/usr/lib/libm.so.6: could not read symbols: Invalid operation
collect2: error: ld returned 1 exit status
Seems like log2(4)will work but I cant pass in a variable?
似乎log2(4)可以工作，但我不能传入一个变量？
回答by Shafik Yaghmour
In in order to link libmyou need to add -lmargument, as this document; MPI under Linux in the Math Departmentsays:
为了链接，libm您需要添加-lm参数，如本文档；数学系 Linux 下的 MPI说：
If your code includes mathematical functions (like exp, cos, etc.), you need to link to the mathematics library libm.so. This is done, just like for serial compiling, by adding -lm to the end of your compile command, that is,
mpicc -o sample sample.c -lm
如果您的代码包含数学函数（如 exp、cos 等），则需要链接到数学库 libm.so。这样做，就像串行编译一样，通过在编译命令的末尾添加 -lm，即，
mpicc -o 示例 sample.c -lm
