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Bug 4311 - warnings when building against libpng-1.4/1.5
Summary: warnings when building against libpng-1.4/1.5
Status: RESOLVED FIXED
Alias: None
Product: SDL_image
Classification: Unclassified
Component: misc (show other bugs)
Version: unspecified
Hardware: All All
: P2 normal
Assignee: Ozkan Sezer
QA Contact: Sam Lantinga
URL:
Keywords:
Depends on:
Blocks:
 
Reported: 2018-10-13 12:20 UTC by Ozkan Sezer
Modified: 2018-10-23 20:01 UTC (History)
0 users

See Also:

Attachments
IMG_png warnings patch (8.01 KB, patch)
2018-10-13 12:20 UTC, Ozkan Sezer 		Details | Diff
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Description Ozkan Sezer 2018-10-13 12:20:06 UTC 
Created attachment 3371 [details]
IMG_png warnings patch

When building against libpng-1.4/1.5 with --disable-png-shared, warnings
are emitted:
I20/IMG_png.c:145: warning: assignment from incompatible pointer type
I20/IMG_png.c:146: warning: assignment from incompatible pointer type
I20/IMG_png.c:147: warning: assignment from incompatible pointer type
I20/IMG_png.c:148: warning: assignment from incompatible pointer type

Some libpng functions take non-const args in 1.2..1.5, but take const
args in 1.6.  To make it worse, some funcs, e.g. png_get_PLTE(), take
const args in 1.4..1.5 but take non-const args in 1.6+, like:
1.4/1.5: (png_const_structp , png_const_infop, png_colorp *, int *)
1.6/1.7: (png_const_structrp, png_inforp     , png_colorp *, int *)

I came up with the following quick'n'dirty patch, which adds noconst15
and noconst16 to affected function pointer typedefs:
noconst15: version < 1.6 doesn't have const, >= 1.6 adds it
noconst16: version < 1.6 does have const, >= 1.6 removes it

Should I apply, or should we live with the warnings (which would break
builds if one uses -Werror) ?
Comment 1 Ozkan Sezer 2018-10-23 20:01:18 UTC 
Went ahead and applied this:
http://hg.libsdl.org/SDL_image/rev/89225c8816d6
http://hg.libsdl.org/SDL_image/rev/fa3c53a205a9