/in/foo.c: In function 'is_symmetric':
/in/foo.c:10:5: warning: implicit declaration of function 'strrev' [-Wimplicit-function-declaration]
     strrev(t); //反转临时空间中的串
     ^
/tmp/ccRwIdzk.o: In function `is_symmetric':
foo.c:(.text+0x32): undefined reference to `strrev'
collect2: error: ld returned 1 exit status