Hi all ~ I have #include <string.h> , but why am I still can't declare string ? When I compile my code ,show the error msg as follows : root@acer:~/probeServer# gcc probec.c -o probec -lm -lpthread probec.c:1:18: error: string: No such file or directory probec.c: In function 'main': probec.c:458: error: 'string' undeclared (first use in this function) probec.c:458: error: (Each undeclared identifier is reported only once any help will be appreciated !! vinod