gdb 调试程序时出现下面信息：
GNU gdb Red Hat Linux (5.3post-0.20021129.18rh)
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This GDB was configured as "i386-redhat-linux-gnu"...(no debugging symbols found)...
然后（gdb）l 出现
No symbol table is loaded. Use the "file" command.
问题出现的原因：
编译时未加调试选项（(g)cc/g++ -g ... ）