c - Read from a pipe(FIFO) then comparing string -

i'm reading pipe.

char buf[255];  while((nbytes = read(fd,buf,sizeof(buf)) > 0)) // fd opened pipe         {            if(strcmp(buf,"in")==0){             printf("%s\n", "set in");           }           if(strcmp(buf,"out")==0){             printf("%s\n", "set out");           } } 

now when write pipe via terminal

echo "out" > /path/to/fifo 

the output i'm getting is: "set in"

all things type "set in" output. how can compare string read pipe?

you treating read data string (by passing strcmp()), there no guarantee input data 0-terminated. in particular, read() doesn't 0-terminate data, fill entire buffer data if possible.

you need yourself, modifying read call like:

while((nbytes = read(fd, buf, sizeof buf - 1)) > 0 ) // fd opened pipe {   buf[nbytes - 1] = '\0'; 

note size passed read() has shrunk make space terminator, , add it.

also note corrected parentheses in while, mentioned in comment @ahmedmasud above. that's point, forgot emphasize it.

update: mentioned xaxxon's answer, data delivered in unpredictable chunks, protocol might useful. easiest protocol textual data flowing on pipe (of course?) line-based. mean should collect data until detect end-of-line character. when do, parse contents of buffer, clear it.