Thread: Function not working how it should.

I have the following code, which tokenises a file of the form:

Code:

Air density (kg/m3) = 1.225
Mass (kg) = 500
Engine power (HP) = 100
etc.

Code:

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

// FUNCTIONS

int linecount(char filename[40])
  {
    FILE *countfile;
    int ch=0;
    int lineno=0;
    countfile=fopen(filename,"r");
    // Count number of lines and length of file      
    while ((ch = fgetc(countfile)) != EOF) if (ch == '\n') ++lineno;
    fclose(countfile);
    return (lineno);
  }

// Checks if import file has been opened correctly.
void importnullcheck(char filename[30])
  {
    FILE *fileopen;
    fileopen=fopen(filename,"r");

    if (fileopen==NULL) fprintf(stdout,"Could not open %s file to read.  Check the filename is correct.\n",filename);
      
    fclose(fileopen);
  }

main()
  {

    char delims[]="=";
    char paramfilename[20],line[128];
    char *param;
    int paramlineno,i;
    FILE *parameters;
    float m,rho,P;

    fprintf(stdout,"\nType in the name and extension of the aircraft data file e.g. param.txt\n");
    scanf("%25s",paramfilename);
    importnullcheck(paramfilename);
    paramlineno=linecount(paramfilename);

    // Open parameters file

    parameters=fopen(paramfilename,"r");
    fseek(parameters, 0, SEEK_SET);
    i=0;
    while(fgets(line,sizeof line,parameters) !=NULL)
      {
	param=strtok(line,delims);

	if (strcmp("Mass (kg) ",param)==0)
	    { param=strtok(NULL,delims);
	      m=atof(param);} 
       if (strcmp("Air density (kg/m3) ",param)==0)
	    { param=strtok(NULL,delims);
	      rho=atof(param);}	    
	if (strcmp("Engine power (HP) ",param)==0)
	    { param=strtok(NULL,delims);
	      P=atof(param);}

       // etc. -about 30 different parameters.

      }

        fprintf(stdout,"Air density is %lf kg/m3\n",rho);
	fprintf(stdout,"Mass is %lf kg\n",m);
	fprintf(stdout,"Power is %lf HP\n",P);
        // etc.

  fclose(parameters);
  return(0);
      }

The output when this is run is:

Code:

Type in the name and extension of the aircraft data file e.g. param.txt
param.txt
Air density is 1.225000 kg/m3
Mass is 500.000000 kg
Power is 100.000000 HP

This is correct. What's the reason the above works, but putting it in a function:

Code:

// FUNCTION

float ftokencomp(char string[12],char *comparison)
  {
    char delims[]="=";
    
    if (strcmp(string,comparison)==0) comparison=strtok(NULL,delims);
    return(atof(comparison));
  }

Then putting

Code:

m=ftokencomp("Mass (kg) ",param); // in the tokenising 'while' loop

fails? It compiles but the output is now

Code:

Type in the name and extension of the aircraft data file e.g. param.txt
param.txt
Air density is 1.225000 kg/m3
Mass is 0.0000000 kg
Power is 100.000000 HP

Obviously something is wrong with my function, can anyone see the problem?

Thanks in advance.

Can you post the code using the function? I'm curious as to if you are still calling strtok() for the first time on this line.

Code:

param=strtok(line,delims);

Also, atof() for me does not have any type that returns a float, only doubles. Maybe you're compiler/environment is different, but it does hurt to do

Code:

return (float)atof(param);

Since your "Mass (kg) " line is first I suspect the string compare is not working like you want. atof() is probably returning zero because strncmp() is never returning 0, so the strtok() in the function is never getting executed.

Thanks for the quick response. Yep, the code with the function implemented is:

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <math.h>
#include <complex.h>
#include "performancefunctions.h"

int linecount(char filename[40])
  {
    FILE *countfile;
    int ch=0;
    int lineno=0;
    countfile=fopen(filename,"r");
    // Count number of lines and length of file      
    while ((ch = fgetc(countfile)) != EOF) if (ch == '\n') ++lineno;
    return (lineno);
  }

// Checks if import file has been opened correctly.
void importnullcheck(char filename[30])
  {
    FILE *fileopen;
    fileopen=fopen(filename,"r");

    if (fileopen==NULL) fprintf(stdout,"Could not open %s file to read.  Check the filename is correct.\n",filename);
      
    close(fileopen);
  }

main()
  {

    char delims[]="=";
    char paramfilename[20],line[128];
    char *param;
    int paramlineno,i;
    FILE *parameters;
    float m,rho,P;

    fprintf(stdout,"\nType in the name and extension of the aircraft data file e.g. param.txt\n");
    scanf("%25s",paramfilename);
    importnullcheck(paramfilename);
    paramlineno=linecount(paramfilename);

    // Open parameters file

    parameters=fopen(paramfilename,"r");
    fseek(parameters, 0, SEEK_SET);
    i=0;
    while(fgets(line,sizeof line,parameters) !=NULL)
      {
	param=strtok(line,delims);

	m=ftokencomp("Mass (kg) ",param);

	/*if (strcmp("Mass (kg) ",param)==0)
	    { param=strtok(NULL,delims);
	      m=atof(param);} */
       if (strcmp("Air density (kg/m3) ",param)==0)
	    { param=strtok(NULL,delims);
	      rho=atof(param);}	    
	if (strcmp("Engine power (HP) ",param)==0)
	    { param=strtok(NULL,delims);
	      P=atof(param);}

       // etc. -about 30 different parameters.

      }

        fprintf(stdout,"Air density is %lf kg/m3\n",rho);
	fprintf(stdout,"Mass is %lf kg\n",m);
	fprintf(stdout,"Power is %lf HP\n",P);
        // etc.

  fclose(parameters);
  return(0);
      }

As you can see, I've only used the function on mass, which is why the other two are still working. The initial strtok appears to be working ok, for the other two parameters at least!

I've changed the function to

Code:

float ftokencomp(char string[12],char *comparison)  // also tried definition as 'double'
  {
    char delims[]="=";
    float newfloat;  // also tried definition as 'double'
    
    if (strcmp(string,comparison)==0) comparison=strtok(NULL,delims);
    newfloat=atof(comparison);
    return(newfloat);
  }

as what you said about returning the float made sense, still no luck though. I agree that it isn't, but any ideas why the strtok in the function isn't getting executed, when it runs fine when not in the function?

Edit: Also, I'm using the GCC compiler in Linux.