Re: About str2double() and exponent identifier

[José Luis García Pallero]

El vie., 10 abr. 2020 a las 13:40, Anthony Tedde
(<address@hidden>) escribió:
>
> Hello,
>
>
> It seems to me that there is an inconsistency, especially because the 
> documentation of the str2double function mentions :
>
> <<
>
> @code{str2double} can replace @code{str2num}, and it avoids the security risk 
> of using @code{eval} on unknown data.
>
> >>
>
>
> The issue occurs because c++ does not understand the char 'd' as the exponent 
> 'e' when converting an istringstream to a double by using the overloaded 
> operator>>.

Yes, the function strtod() in C has the same behavior: only
understands 'e', and 'E' as exponent indicator

>
>
> This inconsistency could be fixed by inserting the following lines after the 
> line 464 in liboctave/util/oct-string.cc:
>
>
> std::size_t dpos = str.rfind('d');
>
> if( dpos != std::string::npos){
>
>   str.replace (dpos, 1, 1, 'e');
>
> }

I think it should be also tested the possibility of 'D' (uppercase) as
identifier, as it is also common in Fortran as the lowercase version
'd'

>
>
> Could it be an acceptable solution to a feature request ?
>
> Anthony
>
>
> On Fri, 10 Apr 2020 at 08:05, Ian McCallion <address@hidden> wrote:
>>
>> On Fri, 10 Apr 2020 at 01:47, José Luis García Pallero <address@hidden> 
>> wrote:
>>>
>>> Hello,
>>>
>>> I've noted that the function str2double() only works with exponent
>>> identifier as 'e' or 'E', but not with 'd' or 'D', that are common
>>> identifiers in files generated using Fortran. Then
>>>
>>> str2double('1e2') is 100, but
>>> str2double('1d2') is NaN
>>>
>>> This behavior is the same in Octave as well as Matlab. Exists any
>>> technical reason in order to not consider the identifiers 'd' or 'D'
>>> for the conversion of the reason of the Octave's behavior is for
>>> matching the Matlab's one?
>>>
>>> I find str2double() more convenient in a task than str2num() as the
>>> first one is faster, but my dataset uses 'D' as exponent identifier
>>
>>
>> str2double is a compiled function, but str2num uses eval which will be a lot 
>> slower as you say.
>>
>> You would almost certainly find it faster to first replace 'd' with 'e'. 
>> e.g.:
>>
>> function d= mystr2double(d)
>>    d(d == 'd')='e';
>>    d = str2double(d);
>> endfunction
>>
>> Cheers... Ian



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José Luis García Pallero
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