conversion of types.

[jj_76]

hello,
I have a data file with several columns consisting of double values. I
am reading the whole row as a string using fgets(). I want to convert
each column back into a double. It seems atof() converts only the first
column and strtod() also does the same. Is there any other way ?
thanks
------------
FILE *fp1;
char thing1[61];
double mtot;

fgets(thing1,61,fp1);
mtot = atof(thing1);

[spibou]

jj_76 wrote:

hello,
I have a data file with several columns consisting of double values. I
am reading the whole row as a string using fgets(). I want to convert
each column back into a double. It seems atof() converts only the first
column and strtod() also does the same. Is there any other way ?

Pass successively a pointer to the beginning of each column to
strtod() and store the result in whatever way you want.

Spiros Bousbouras

[Joe Wright]

jj_76 wrote:

hello,
I have a data file with several columns consisting of double values. I
am reading the whole row as a string using fgets(). I want to convert
each column back into a double. It seems atof() converts only the first
column and strtod() also does the same. Is there any other way ?
thanks
------------
FILE *fp1;
char thing1[61];
double mtot;

fgets(thing1,61,fp1);
mtot = atof(thing1);

What is the actual format of the file? Are there a fixed number of
columns (fields) per row? How are the fields delimited?

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[CBFalconer]

Joe Wright wrote:

jj_76 wrote:

>I have a data file with several columns consisting of double
values. I am reading the whole row as a string using fgets().
I want to convert each column back into a double. It seems atof()
converts only the first column and strtod() also does the same.
Is there any other way ?

FILE *fp1;
char thing1[61];
double mtot;

fgets(thing1,61,fp1);
mtot = atof(thing1);

What is the actual format of the file? Are there a fixed number
of columns (fields) per row? How are the fields delimited?

What does that matter, given his description as a set of columns?
The description of strtod() (below, from N869) should suffice for
the OP, since the returned endptr will always describe from where
to extract the next value.

7.20.1.3 The strtod, strtof, and strtold functions

Synopsis

[#1]

#include <stdlib.h>
double strtod(const char * restrict nptr,
char ** restrict endptr);
float strtof(const char * restrict nptr,
char ** restrict endptr);
long double strtold(const char * restrict nptr,
char ** restrict endptr);

Description

[#2] The strtod, strtof, and strtold functions convert the
initial portion of the string pointed to by nptr to double,
float, and long double representation, respectively. First,
they decompose the input string into three parts: an
initial, possibly empty, sequence of white-space characters
(as specified by the isspace function), a subject sequence
resembling a floating-point constant or representing an
infinity or NaN; and a final string of one or more
unrecognized characters, including the terminating null
character of the input string. Then, they attempt to
convert the subject sequence to a floating-point number, and
return the result.
--
Chuck F (cb********@yahoo.com) (cb********@maineline.net)
Available for consulting/temporary embedded and systems.
<http://cbfalconer.home.att.netUSE maineline address!

[Joe Wright]

CBFalconer wrote:

Joe Wright wrote:

>jj_76 wrote:

>>I have a data file with several columns consisting of double
values. I am reading the whole row as a string using fgets().
I want to convert each column back into a double. It seems atof()
converts only the first column and strtod() also does the same.
Is there any other way ?

FILE *fp1;
char thing1[61];
double mtot;

fgets(thing1,61,fp1);
mtot = atof(thing1);

What is the actual format of the file? Are there a fixed number
of columns (fields) per row? How are the fields delimited?

What does that matter, given his description as a set of columns?
The description of strtod() (below, from N869) should suffice for
the OP, since the returned endptr will always describe from where
to extract the next value.

[ snip ]

Hi Chuck, welcome back.

What does the file format matter? You cannot make sense of a file unless
you know exactly how it was written. I might write doubles to a binary
file where each double is eight bytes long. For you to read that file
successfully you'd have to know that. Such things as endianness become
important. Certainly fgets() is useless on a binary file of doubles.

So now, assuming a text file and fprintf() we might write two doubles, 3
and 4..

3.000000
4.000000

...which are essentially concatenated to "3.0000004.000000" and so on.
What is strtod() and company to do with this? Nothing rational. You need
to delimit the values with an 'out-of-bound' character like '|' or
something. If the above string were delimited like..

"3.000000|4.000000|"

...then we know what to do.

You have to know the format of the file you are reading.

--
Joe Wright
"Everything should be made as simple as possible, but not simpler."
--- Albert Einstein ---

[trm]

jj_76 schrieb:

hello,
I have a data file with several columns consisting of double values. I
am reading the whole row as a string using fgets(). I want to convert
each column back into a double. It seems atof() converts only the first
column and strtod() also does the same. Is there any other way ?
thanks
------------
FILE *fp1;
char thing1[61];
double mtot;

fgets(thing1,61,fp1);
mtot = atof(thing1);

What did you expect it to do? atof() can only return a single value,
which you can store in a single variable, as you've shown. So it isn't
possible for it to convert more than one column.

Perhaps you were expecting it to "consume" the string, so that
multiple calls in sequence would convert the values of the other
columns? That just won't work. Consider that the parameter to atof()
is a string, that is, a (const char *). There simply isn't any way for
the function to alter the pointer so that the change is propagated
back up to the caller.

However, strtod() will do what you need. See CBFalconer's reply
to learn how it works.