can't get string conversion strtod in c

Question

Could somebody help me(sorry for the english), Im trying to convert a string to a double but when I can't get it here's my code(thank you, I'll appreciate help so much):

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

#define MAX_LONG 5

char bx[MAX_LONG];
double cali=0;

int main() {
scanf("%c",bx);
cali = strtod(bx,NULL);
printf("%f",cali);
return 0;
}

when I input a value greater than 10 in the output it just print the first number like this:

 input: 23
 output: 2.00000
 input: 564
 output: 5.00000

Why don't you use `scanf("%lf", &cali)`? – user12205 Apr 25 '15 at 00:07 — user12205, Apr 25 '15 at 00:07

Iharob Al Asimi · Accepted Answer · 2015-04-25T00:31:29.050

2

The scanf() specifier you are using is wrong, unless you specify a number of characters, but then the array will not be nul terminated, I suggest the following

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

int main() 
{
    char   bx[6]; /* if you want 5 characters, need an array of 6
                   * because a string needs a `nul' terminator byte
                   */
    double cali;
    char  *endptr;

    if (scanf("%5s", bx) != 1)
    {
        fprintf(stderr, "`scanf()' unexpected error.\n");
        return -1;
    }

    cali = strtod(bx, &endptr);
    if (*endptr != '\0')
    {
        fprintf(stderr, "cannot convert, `%s' to `double'\n", bx);
        return -1;
    }        
    printf("%f\n", cali);
    return 0;
}

edited Apr 25 '15 at 00:31

answered Apr 24 '15 at 23:13

Iharob Al Asimi

52,653
6
59
97

Thank you so much I'll implement this code in my program (: – user2461687 Apr 24 '15 at 23:18
this is great (I'm trying to understand this is my first program ) Thanks – user2461687 Apr 24 '15 at 23:20
You need to read the manuals or standard specification for the functions to really learn how to used them, for example `scanf()` is misused in many books. – Iharob Al Asimi Apr 24 '15 at 23:21
Ok, I'll download one – user2461687 Apr 24 '15 at 23:25
I ran the code but it doesn't work always print "`scanf()' unexpected error." :c – user2461687 Apr 24 '15 at 23:29
@user2461687 I am sorry.. I typed `==` by mistake. – Iharob Al Asimi Apr 24 '15 at 23:52
@iharob Note that your second `fprintf()` causes undefined behaviour. (You have `%s` but no other arguments.) – user12205 Apr 25 '15 at 00:05
thank you, I just need to change scanf("%s",bx) from your code, it´s working now I can get done my homework C: – user2461687 Apr 25 '15 at 00:13
@user2461687 **Do not** use `scanf("%s", bx);` be cause you might overflow the `bx` buffer, it may seem to work, but it could suddenly break because it's not working, if it does is just because you are lucky. Increase the size of `bx`, and change `"%5s"` to `"%Ns` where `N` should be the number of elements of `bx` minus 1. – Iharob Al Asimi Apr 25 '15 at 16:23

score 0 · Answer 2 · answered Apr 25 '15 at 01:14

0

You should try this changes to make it work.

First: Change

scanf("%c",bx); /*Here you're reading a single char*/

To this:

scanf("%s",bx);/*Now you're reading a full string (No spaces)*/

Second: Change

cali = strtod(bx,NULL);

To this:

cali = atof(bx);

This i think will work perferct For you.

answered Apr 25 '15 at 01:14

Francisco Collado Arocha

46
1
7

You generally do not want to discourage someone from using a function such as `strtod` that provides far superior error checking in the event of a conversion failure than does `atof` which provides ..... none. You want to help them understand how to properly check the results of `errno`, the value of `endptr` and whether a **high/low infinite value** was returned. – David C. Rankin Apr 25 '15 at 04:08

can't get string conversion strtod in c

2 Answers2