Thread: strtok and strcmp pointer issues question

Hi everyone,
I want to tokenise a text file with around 20 lines, and as the lines could be moved around, I want it to check the tokens for a certain word and if it contains that word, I want to equate the second token to it.

That's probably confusing so here's an example (condensed) text file:

Code:

Mass (kg) = 500

Wingspan (m) = 8.23

Wing area (m2) = 11.4

and the code I'm currently fighting with is

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>

main ()

{
       char *mass;
       float m;
       char *WINGSPAN;
       float wingspan;
       char *s;
       float S;
       char *param[40];
       char *param2[40];

/* Open and print number of lines in file - all works fine */

 /* Problem area */

 /* tokenise to find actual parameters */
char delims[]="="; 

for (i=1;i<=lineno+1; i++)
	{
	   param[i]=strtok(arra[i],delims);
	   param2[i]=strtok(NULL,delims);

	  if (strcmp('Mass*',param[i])==0) mass=param2[i];
	  if (strcmp('Wingspan*',param[i])==0) WINGSPAN=param2[i];
	  if (strcmp('Wing area*',param[i])==0) s=param2[i];
	}

m=atof(mass);
printf("Mass is %f kg\n",m); 

wingspan=atof(WINGSPAN);
printf("Wingspan is %f m\n",wingspan);

S=atof(s);
printf("Wing area is %f m2\n",S);

}

I've gotten around it by using

Code:

for (i=1;i<=lineno+1; i++)
	{
	   param[i]=strtok(arra[i],delims);
	   param2[i]=strtok(NULL,delims);
        }

mass=param2[0];
m=atof(mass);
printf("Mass is %f kg\n",m); 

WINGSPAN=param2[2];
wingspan=atof(WINGSPAN);
printf("Wingspan is %f m\n",wingspan);

s=param2[4];
S=atof(s);
printf("Wing area is %f m2\n",S);

but this isn't helpful when lines are added to the file or switched around!

Error messages are:
weightest.c:204:15: warning: character constant too long for its type
weightest.c: In function ‘main’:
weightest.c:204: warning: passing argument 1 of ‘strcmp’ makes pointer from integer without a cast
weightest.c:204: error: incompatible types in assignment
weightest.c:205:15: warning: character constant too long for its type
weightest.c:205: warning: passing argument 1 of ‘strcmp’ makes pointer from integer without a cast
weightest.c:206:15: warning: character constant too long for its type
weightest.c:206: warning: passing argument 1 of ‘strcmp’ makes pointer from integer without a cast
weightest.c:211: warning: passing argument 1 of ‘atof’ from incompatible pointer type

There's obviously something wrong with how I've declared the pointers but I'm really not sure how to fix it so any advice would be gratefully received! Thank you.

At a glance, you use double quotes for strings, not single quotes.

"string"

not

'string'


Quzah.

Arrays start at zero, not one, so you should be starting your loop with i=0. You never check to see if mass is not-NULL before you use it. You pretty much don't do that ever. You should really be doing two things: (1) makes sure you initialize your pointers before using them, (2) check to see they're not-null before trying to dereference them.


Quzah.

At which point is it segfaulting?

Code:

for( x = 0; x < FOO; x++ )
{
    p[ x ] = strtok( stuff );
    if( p[ x ] )
    {
        NOW do stuff with p[ x ]
    }

}

Like I said, you need to make sure your functions are doing what you expect before you start blindly using the arrays you expect to have stuff in them. Also pay attention to the last line of output you actually see, that'll give you a good indicator of where things are gone wrong.


Quzah.

Originally Posted by snoikey

You don't need the brackets round the 'if' statement if there's only one line involved.. only learnt that yesterday from my project supervisor, this is just one part of a program that's over 1000 lines and space-saving is also effort-saving when I need to find particular sections.

Yes, it is true that if you leave out the braces, you may be able to shorten your program in terms of number of lines, but this does not necessarily make it easier to find particular sections, and in fact if you try and "squeeze" your source code, you may find it even more difficult to read and hence to find anything at a glance. Furthermore, because indentation, however important, is not what the compiler actually uses to determine scope, keeping "superfluous" braces can be useful to avoid bugs that may arise during maintenance.

A point that you want to take note: programs that are "over 1000 lines" are actually quite common. I noticed that your sample code includes none of your own headers and comes with no other function declarations. If you want to be able to handle larger programs, then you should start defining other functions that do one thing and do it well (in separate source files, if necessary).

You completely missed the point I was making. You need to check to see that your variables have valid data before you start fiddling with them. Way to miss the obvious and distract yourself because I happen to have included a pair of braces. I suspect you'll be working on this project for a very long time.


Quzah.

Well, what is arra? The first place where it appears in your code snippet, it is used in strtok, which implies that it must have been used earlier, otherwise it would be an example of the kind of mistake that quzah is talking about.