# SDL: Initialize constant memory stream size

**URL:** <https://discourse.libsdl.org/t/sdl-initialize-constant-memory-stream-size/69394>\
**Category:** SDL Commits\
**Created:** [September 24, 2026, 9:45pm UTC](https://discourse.libsdl.org/t/sdl-initialize-constant-memory-stream-size/69394 "2026-09-24T21:45:13Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![SDLPushPostBot](https://discourse.libsdl.org/user_avatar/discourse.libsdl.org/sdlpushpostbot/32/4370_2.png) [@SDLPushPostBot](https://discourse.libsdl.org/u/SDLPushPostBot)\
**Post date:** [September 24, 2026, 9:45pm UTC](https://discourse.libsdl.org/t/sdl-initialize-constant-memory-stream-size/69394/1 "2026-09-24T21:45:13Z")

</div>

> <https://github.com/libsdl-org/SDL/commit/70e125ba8ef21813c34bb258366a4420e7f52327>
>
> Preserve the supplied size when creating a constant memory stream so lazy
> proper…ties report the correct buffer size. Extend the existing constant
> memory test to check that property.

```diff
From 70e125ba8ef21813c34bb258366a4420e7f52327 Mon Sep 17 00:00:00 2001
From: alistanis <[EMAIL REDACTED]>
Date: Thu, 24 Sep 2026 12:38:48 -0400
Subject: [PATCH] Initialize constant memory stream size

Preserve the supplied size when creating a constant memory stream so lazy
properties report the correct buffer size. Extend the existing constant
memory test to check that property.
---
 src/io/SDL_iostream.c | 1 +
 test/testautomation_iostream.c | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/src/io/SDL_iostream.c b/src/io/SDL_iostream.c
index 3382201b0476e..d8a152ed9b76b 100644
--- a/src/io/SDL_iostream.c
+++ b/src/io/SDL_iostream.c
@@ -1253,6 +1253,7 @@ SDL_IOStream *SDL_IOFromConstMem(const void *mem, size_t size)
     iodata->base = (Uint8 *)mem;
     iodata->here = iodata->base;
     iodata->stop = iodata->base + size;
+ iodata->size = size;
 
     SDL_IOStream *iostr = SDL_OpenIO(&iface, iodata);
     if (!iostr) {
diff --git a/test/testautomation_iostream.c b/test/testautomation_iostream.c
index 240aaf9f0d457..45d60771e81bb 100644
--- a/test/testautomation_iostream.c
+++ b/test/testautomation_iostream.c
@@ -385,6 +385,7 @@ static int SDLCALL iostrm_testMem(void *arg)
 static int SDLCALL iostrm_testConstMem(void *arg)
 {
     SDL_IOStream *rw;
+ SDL_PropertiesID props;
     int result;
 
     /* Open handle */
@@ -400,6 +401,11 @@ static int SDLCALL iostrm_testConstMem(void *arg)
     /* Run generic tests */
     testGenericIOStreamValidations(rw, false);
 
+ /* Verify properties preserve the supplied buffer size. */
+ props = SDL_GetIOProperties(rw);
+ SDLTest_AssertCheck(props != 0, "Get constant memory stream properties");
+ SDLTest_AssertCheck(SDL_GetNumberProperty(props, SDL_PROP_IOSTREAM_MEMORY_SIZE_NUMBER, -1) == (Sint64)(sizeof(IOStreamHelloWorldCompString) - 1), "Verify memory size property matches the supplied buffer size");
+
     /* Close handle */
     result = SDL_CloseIO(rw);
     SDLTest_AssertPass("Call to SDL_CloseIO() succeeded");

```