What is wrong with this C code ?

indian · 04-14-2005, 11:45 PM

HI,
I am trying to read come numbers from a text file and than convert those numbers to floats.Here is my code,Everything looks fine but still I am not able to understand that why it is giving segmentation fault:-

AFTER DARK HELMET's SUGESTION I HAVE MODIFIDE THE CODE,BUT IT IS STILL GIVING SEGMENTATION FAULT

Hereis the modified code

Code:

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

main()
{
    FILE *fs;
    char ch,d;
    char str[20];

    fs=fopen("text","r");
    int i;
    while((ch=fgetc(fs))!=EOF)
    {
        if( (ch!='\t') || (ch!='\n'))
        {
            i=0;
            str[i]=ch;
            while((ch!='\t') || (ch!='\n') || (ch!=EOF))
            {
                ch=fgetc(fs);
                str[i]=ch;
                i++;
            }
            str[i]='\0';
            func(str);
        }
        else
        {
            continue;
        }
    }
}

func(char *str)
{
        float a;
        a=atof(str);
        printf("%f\t",a);
}

I hope the code is clear to all

regards

Dark_Helmet · 04-15-2005, 12:29 AM

First, I think your if() statement is incorrect. Shouldn't this:

Code:

if(ch!='\t' ||ch!='\n')

be this:

Code:

if( (ch != '\t' ) && ( ch != '\n' ) )

The way you currently have it, you will always enter the loop. If ch equals '\t' then it is definitely not equal to '\n' and vice versa. It will always enter that if block.

Second: this is probably the cause of your segmentation fault. Earlier in your program, you do this:

Code:

while((ch=fgetc(fs))!=EOF)

Then later, you start reading from the file again with:

Code:

while((ch=fgetc(fs))!='\t')

So, why don't you check for EOF in the second while loop? Isn't it possible you could reach the end of the file in the second loop? You need to change the condition of your second while loop to check for '\t' and EOF.

Roptaty · 04-15-2005, 01:34 AM

There are several bugs in this code.

Code:

    fs=fopen("text","r");   #1
    int i;
    while((ch=fgetc(fs))!=EOF)
    {
        if( (ch!='\t') || (ch!='\n'))
        {
            i=0;
            str[i]=ch; 
            while((ch!='\t') || (ch!='\n') || (ch!=EOF)) 
            {
                ch=fgetc(fs); #2
                str[i]=ch;
                i++;
            }
            str[i]='\0';
            func(str);
        }
        else
        {
            continue; #3
        }
    }

#1: You dont check if the file was opened successfully.
#2: In the first run, you check the previous character which you have already checked..
n the first run, you will also overwrite the old str[i] value. Since the value of the i variable is the same as before. You fail to check the value of ch here as well.
#3: Not really needed

One tip: Try using a debugger to check for flaws in your code. I've had some d'oh-experiences with my own code.

Dark_Helmet · 04-15-2005, 02:15 AM

indian:
I see you edited your code and didn't post a reply. There's no way for people to know you've updated it. People don't get email alerts when you edit a post; only when there's a reply.

I have to repeat the first point I made previously: your conditions in the if-statement and while loops are still wrong. You are using the logical OR operator ( || ) when you should be using the logical AND operator ( && ). The following if statement will never evaluate to false:

Code:

if( (ch!='\t') || (ch!='\n'))

Similarly, your inner while loop will never exit:

Code:

while((ch!='\t') || (ch!='\n') || (ch!=EOF))

Change the logical OR's to logical AND's.

indian · 04-15-2005, 03:49 AM

Ya DH...now it is running..

..there were definately some problem with while loops ..and thanks Roptaty for good suggestions...I shud had used AND isntead of OR .

Thanks again to both of u..

max_rsr · 04-15-2005, 08:53 AM

ok here's your complete working code .there were a few redundancies in your code
I have tested the program it should work
this should solve your problem.

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

void func(char str[]);

int main()
{
int i = 0;
char ch;
char str[20];
FILE *fs;

fs = fopen("text","r");
if(!fs) {
printf("\ncannot open input file");
exit(1);
}

while((ch = getc(fs))!=EOF) {
if(ch!= ' '&&ch!= '\t'&&ch!='\n')
str[i] = ch;
i++;
}

str[i] = '\0';

func(str);
}

void func(char str[])
{
float a;

a = atof(str);
printf("\n%f",a);

}

Hope u appreciate it.

andrewnow · 04-15-2005, 09:48 PM

//i changed your code as follows:

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

main()
{
FILE *fs;
char ch,d;
char str[20];

if(!(fs=fopen("text","r")))
{
printf("Cant open file!!(Please check that the file is exist or readable)\n");
exit(-1);
}
int i=0;
while((ch=fgetc(fs))!=EOF)
{
if( (ch!='\t') && (ch!='\n'))
{
i=0;
str[i++]=ch;
while((ch!='\t') && (ch!='\n') && (ch!=EOF))
{
ch=fgetc(fs);
str[i++]=ch;
}
str[i]='\0';
func(str);
printf("the sting is=====>>%s\n",str);
}
}
printf("\n");
}

func(char *str)
{
float a;
a=atof(str);
printf("%f\t",a);
}
//it works well in my computer

indian · 04-16-2005, 03:37 AM

thanks Max and Andrew....by the way here is one more question..I frequently needs to read words from some text file and than convert it into Int or Float..

SO now what I want is can I make this a library ?

I mean I can definately make it a header file and always include it but can't I include this file in some thing like My_lib.h ?

so whenever I uses #include<My_lib.h> than I can use this code

..I don't want to use this as a header file but as a library.

Thanks again

andrewnow · 04-16-2005, 04:42 AM

1.change the name of your main() function.as follows:
#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<math.h>

void trans_to_float()
{
FILE *fs;
char ch,d;
char str[20];

if(!(fs=fopen("text","r")))
{
printf("Cant open file!!(Please check that the file is exist or readable)\n");
exit(-1);
}
int i=0;
while((ch=fgetc(fs))!=EOF)
{
if( (ch!='\t') && (ch!='\n'))
{
i=0;
str[i++]=ch;
while((ch!='\t') && (ch!='\n') && (ch!=EOF))
{
ch=fgetc(fs);
str[i++]=ch;
}
str[i]='\0';
func(str);
printf("the sting is=====>>%s\n",str);
}
}
printf("\n");
}

func(char *str)
{
float a;
a=atof(str);
printf("%f\t",a);
}

2.compile your code with such command:gcc -c trans_to_float.c
3.edit a header file as it's name is: My_lib.h
4.ar crv My_lib.a trans_to_float.o
5.ranlib My_lib.a
6.it's ok now.you can include this function by #include "My_lib.h"
7.gcc -o yourprogram yourprogram.o Mylib.a
8.ok!

it's called "archive". Many books telled about it. You can find this in "Begining of Linux Programming" by Wrox