Recognize if the floating number is valid or not in C

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);
}

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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;
}

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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.

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);

}

---

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).

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Code:

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

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

--
Mats