Recognize if the floating number is valid or not in C

feb0590 · 04-15-2009, 10:59 AM

I can now validate whether a number is a valid float number or not but i'm having problems in getting the values from a text file. Can someone help me?

Code:

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

int check_floatnum(double *output)
{
	double floatnum;
	FILE *fp1;
	char *end, fnum[32];

	if(fgets(fnum, sizeof(fnum), stdin) && !isspace(*fnum) && (*output = strtod(fnum, &end)), ( *end == '\n' || *end == '\0' ))
		printf("VALID\n ");
	else
		printf("INVALID\n ");
}

int main(void)
{
	double floatnum = -12.3;

	do
	{
		fp1 = fopen("C:\\input.txt","r");


	}
	while (check_floatnum(fp1));

	fclose(fp1);
}

MK27 · 04-15-2009, 02:47 PM

You can use fgets to read from a file:

Code:

#include <stdlib.h>

int main() {
        float X;
        char fnum[16];
        FILE *file=fopen("text.file","r");

        fgets(fnum,16,file);  /* use the file stream pointer instead of stdin */
        X=strtof((const char*)fnum,NULL);
        printf("%s%f\n",fnum,X);

        return 0;
}

That presumes that the first thing in the file is a decimal number. If you need to parse it out of other data, then things become more complicated.

feb0590 · 04-16-2009, 04:49 AM

Thank you but i need to pass the values from file to function check_floatnum correctly. The function check_floatnum validates whether the float number from input.txt is a valid floating point number or not. Now, the problem is i cannot pass the values from input.txt to function check_floatnum correctly. Can you please help me? This is the sample values from input.txt:

1.15 VALID
1/2 INVALID

Code:

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

int check_floatnum(double *output)
{
	double floatnum;
	FILE *fp1;
	char *end, fnum[32];

	if(fgets(fnum, sizeof(fnum), fp1) && !isspace(*fnum) && (*output = strtod(fnum, &end)), ( *end == '\n' || *end == '\0' ))
		printf("VALID\n ");
	else
		printf("INVALID\n ");
}

int main(void)
{
	double floatnum = -12.3;
    float X;
    char fnum[16];

	FILE *fp1=fopen("C:\\input.txt","r");

	do
	{	


	}
	while (check_floatnum(fp1));

	fclose(fp1);

}

matsp · 04-16-2009, 04:57 AM

Your code is a bit of a mess:
You are passing a FIEL pointer to a function that expects a double pointer. You then USE FILE *fp1 in the function - this variable has not been initialized and I'm 99.9% sure that the random value that it happens to have is not a valid FILE * that points to the same object that you got from fopen() in main - and I guess that's what you'd actually want to do.

So, first, change the parameter type of your check function so that you pass a FILE * into it [you may need to have a double pointer too, if you need to also pass back the value from the file]. Second, remove the FILE *fp1 from the function, an use the passed in FILE pointer.

You also do not need to use "isspace" to validate your number - strtod() and friends already do that for you:
From man strtod(3)

Quote:

Originally Posted by Manpagez

In any of the above cases, leading white-space characters in the string
(as defined by the isspace(3) function) are skipped. The decimal point
character is defined in the program's locale (category LC_NUMERIC).

Code:

&& (*output = strtod(fnum, &end)), ( *end == '\n' || *end == '\0' )

This is too obfuscated - don't use the comma operator like that. Do you actually know what this does?

--
Mats

04-15-2009, 02:47 PM	#2
MK27 subminimalist Join Date: Jul 2008 Location: NYC Posts: 3,946	You can use fgets to read from a file: Code: #include <stdlib.h> int main() { float X; char fnum[16]; FILE file=fopen("text.file","r"); fgets(fnum,16,file); / use the file stream pointer instead of stdin / X=strtof((const char)fnum,NULL); printf("%s%f\n",fnum,X); return 0; } That presumes that the first thing in the file is a decimal number. If you need to parse it out of other data, then things become more complicated. __________________ Accuracy and integrity mean nothing if you don't make it past the censors...PYTHAGORAS
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04-16-2009, 04:49 AM	#3
feb0590 Registered User Join Date: Apr 2009 Posts: 2	Thank you but i need to pass the values from file to function check_floatnum correctly. The function check_floatnum validates whether the float number from input.txt is a valid floating point number or not. Now, the problem is i cannot pass the values from input.txt to function check_floatnum correctly. Can you please help me? This is the sample values from input.txt: 1.15 VALID 1/2 INVALID Code: #include<stdio.h> #include<stdlib.h> #include<ctype.h> int check_floatnum(double output) { double floatnum; FILE fp1; char end, fnum[32]; if(fgets(fnum, sizeof(fnum), fp1) && !isspace(fnum) && (output = strtod(fnum, &end)), ( end == '\n' \|\| end == '\0' )) printf("VALID\n "); else printf("INVALID\n "); } int main(void) { double floatnum = -12.3; float X; char fnum[16]; FILE fp1=fopen("C:\\input.txt","r"); do { } while (check_floatnum(fp1)); fclose(fp1); }
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