[gdal-dev] Reading a double from file

Andrew C Aitchison andrew at aitchison.me.uk
Tue Jun 16 07:34:09 PDT 2020

Thanks to you both.

On Tue, 16 Jun 2020, Even Rouault wrote:

> On mardi 16 juin 2020 11:02:55 CEST Mateusz Loskot wrote:
>> On Tue, 16 Jun 2020 at 10:08, Andrew C Aitchison <andrew at aitchison.me.uk> wrote:
>>> Does gdal have a standard, endian-independent,
>>> way to read floating point values from file ?
>>> Specifically IEEE-754 little-endian 64bit values.
>>> So far my driver has used a union to "cast" 8 bytes to a double,
>>> but I now discover that, whilst this is valid C, it is not valid C++.
>>> I am looking for a portable way to read such values from file
>>> into a C++ double. This cannot be the first gdal driver to need to do
>>> this.
>> Generally, use std::memcpy or std::copy.
>> Detect if you need to swap bytes and swap bytes.
> A rather compact and portable way:
> double x;
> std::memcpy(&x, ..., sizeof(double));
> CPL_LSBPTR64(&x); // if the ordering in the file is little-endian
> CPL_MSBPTR64(&x); // if the ordering in the file is big-endian
> -- 
> Spatialys - Geospatial professional services
> http://www.spatialys.com

Andrew C. Aitchison					Kendal, UK
 			andrew at aitchison.me.uk

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