Converting a string into a double

Question

I am trying to convert a string (const char* argv[]) to a double precision floating point number:

int main(const int argc, const char *argv[]) {
    int i;
    double numbers[argc - 1];
    for(i = 1; i < argc; i += 1) {
        /* -- Convert each argv into a double and put it in `number` */
    }
    /* ... */
    return 0;
}

Can anyone help me? Thanks

Grrr! No. You want to convert a string, the beginning of which is pointed to, by a const char*, to double — Maciej Hehl, May 23 '10 at 19:01
@Maciej: Nah, every experienced C programmer knows a `const char*` is 99.9% a string. — kennytm, May 23 '10 at 19:07
@Kenny: Sure if it is the second argument of the `main` function. — , May 23 '10 at 19:08
Oh well, I just have a "being an ass day", I guess. I just couldn't resist. — Maciej Hehl, May 23 '10 at 19:18

score 9 · Accepted Answer · edited May 23 '10 at 19:04

9

Use sscanf (Ref)

sscanf(argv[i], "%lf", numbers+i);

or strtod (Ref)

numbers[i] = strtod(argv[i], NULL);

BTW,

for(i = 1; i < argc, i += 1) {
//-----------------^ should be a semicolon (;)

-->

edited May 23 '10 at 19:04

answered May 23 '10 at 18:56

kennytm

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`strtod` did the job. Thanks =D – May 23 '10 at 19:02
Oh, and the `,` instead of a `;` was a typo. – May 23 '10 at 19:05

score 1 · Answer 2 · answered May 23 '10 at 18:57

1

Or use atof

http://www.cplusplus.com/reference/clibrary/cstdlib/atof/

answered May 23 '10 at 18:57

LukeN

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No real reason to use atof anymore with the safer strtod – Martin Beckett May 23 '10 at 19:18

score 1 · Answer 3 · answered May 23 '10 at 18:58

1

You can use strtod which is defined in stdlib.h

Theoretically, it should be more efficient that the scanf-family of functions although I don't think it'll be measurable.

answered May 23 '10 at 18:58

Isak Savo

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score 0 · Answer 4 · answered May 23 '10 at 18:58

0

You haven't said what format the const char*s might be in. Presuming they're text strings like "1.23", then sscanf(argv[i], "%lf", &numbers[i-1]) ought to do the job.

answered May 23 '10 at 18:58

crazyscot

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I think I was referring to the difference between normal and scientific notation. – crazyscot May 11 '17 at 05:23

Converting a string into a double

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