[Lazarus] How to switch a project from 32 to 64 bit (on Windows 7 x64)?

[Werner Pamler]

Am 28.05.2019 um 10:40 schrieb Bo Berglund via lazarus:
> Right now I have the following installed in my Win7 x64 environment:
> Lazarus 1.6
> Lazarus 1.8
> Lazarus 1.8.4 32 bit
> Lazarus 2.0.0 32 bit
> Lazarus 2.0.0 64 bit
>
> All of these have internbal fpc directories containing the
> correspondiing fpc compiler files.

The same with me (plus some more, in particular trunk installations for 
Lazarus and fpc). This is indispensable for testing when your code 
should not be tied to the newest IDE version.

Normally, it is no problem to switch between different versions. But be 
aware: When loading an project in a new version may change the project 
in a way that it is not readable by the old version again. Laz 2.0, for 
example, can add the line "Application.Scaled" to the project unit when 
you use the High-dpi features - this is a problem for 1.6. (You may 
enclose the line by an $IFDEF which helps for some time, but after some 
changes the IDE is very persistent and adds the line again). Or Lazarus 
trunk introduces a new file structure, you must save every new project 
with checed "Maximize compatibility of project files" in "Project 
options" > "Miscellaneous"; otherwise the project will have no files in 
Laz 2.0.2 or older.