Using strcmp() in my cgi code, for an html webpage, is causing a server error - html

Question

I am making an html webpage that uses cgi to access a table/database in mysql. I input a .csv file containing info on my class schedule and the html displays it in the usual schedule table.
My problem is that I can't seem to use strcmp in my parsing cgi as it causes a server error. here is an excerpt of my code where I uses strcmp.
void parse2(char *queu)
{
//---------------------------------------------------------------
char *saveptr[1024];
char *subtoken;
char *Subject;
char *Day;
char *Start;
char *End;
char *Room;
char *Teacher;
int check = 1;
//---------------------------------------------------------------
subtoken = strtok_r(queu, ",", saveptr);
check = strcmp(subtoken, "\0");
printf("%d<br>", check);
if(check == 0){
printf("Error!");
} else {
Subject = subtoken;
Day = strtok_r(NULL, ",", saveptr);
Start = strtok_r(NULL, ",", saveptr);
End = strtok_r(NULL, ",", saveptr);
Room = strtok_r(NULL, ",", saveptr);
Teacher = strtok_r(NULL, ",", saveptr);
printf("%s\n<br/>%s\n<br/>%s\n<br/>%s\n<br/>%s\n<br/>%s\n", Subject, Day, Start, End, Room, Teacher);
//inputsql(Subject, Day, Start, End, Room, Teacher);
}
//---------------------------------------------------------------
}
Note that, I have tested this code and it works fine without me calling strcmp().
I am using strcmp() to prevent a line of unwanted characters, generated after the info when retrieved using POST method, from being entered into my database.
As you can see from the above code, I used strtok() to parse the line of info. Since the line of unwanted characters do not contain a comma (which is my delimiter) it should return a NULL value. correct?
Can anyone help me out? I welcome suggestions to use a different way on solving the problem I chose to solve using strcmp().

Answer 1

I think you should be checking subtoken == NULL, not strcmp(subtoken, "\0") == 0.
"\0" is a string containing a NUL byte, then another NUL (the terminator), so the standard library's string functions will just see an empty string. That's different to a NULL pointer (i.e. a pointer with value zero).
From STRTOK(3):
Each call to strtok() returns a pointer to a null-terminated string
containing the next token. This string does not include the
delimiting byte. If no more tokens are found, strtok() returns NULL.