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iostream: Properly support the "x" mode for SDL_IOFromFile()

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The "x" mode for `fopen()` (open file only if it doesn't exist) used to
be a glibc-exclusive extension, but was later standardized in C11, and
is now also implemented as part of every other widely-used libc:

	* musl: https://git.musl-libc.org/cgit/musl/tree/src/stdio/__fmodeflags.c?id=0ccaf0572e9cccda2cced0f7ee659af4c1c6679a
	* Android Bionic / OpenBSD: 731631f300/libc/upstream-openbsd/lib/libc/stdio/flags.c (86)
	* Apple / FreeBSD: 63976b830a/stdio/FreeBSD/flags.c (L91-L92)

As a result, "x" has already been working on all our automatically
tested platforms that implement `SDL_IOFromFile()` via `fopen()`. So
all we'd be missing for proper support is a Windows implementation
using `CREATE_NEW`, and the documentation that this mode exists and is
intended to work.
This commit is contained in:
nmlgc
2025-10-05 23:15:03 +02:00
committed by Sam Lantinga
parent 87e3250518
commit 8df057fafc
3 changed files with 18 additions and 3 deletions
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4
include/SDL3/SDL_iostream.h
View File

@@ -203,6 +203,8 @@ typedef struct SDL_IOStream SDL_IOStream;
* - "w": Create an empty file for writing. If a file with the same name
* already exists its content is erased and the file is treated as a new
* empty file.
* - "wx": Create an empty file for writing. If a file with the same name
* already exists, the call fails.
* - "a": Append to a file. Writing operations append data at the end of the
* file. The file is created if it does not exist.
* - "r+": Open a file for update both reading and writing. The file must
@@ -210,6 +212,8 @@ typedef struct SDL_IOStream SDL_IOStream;
* - "w+": Create an empty file for both reading and writing. If a file with
* the same name already exists its content is erased and the file is
* treated as a new empty file.
* - "w+x": Create an empty file for both reading and writing. If a file with
* the same name already exists, the call fails.
* - "a+": Open a file for reading and appending. All writing operations are
* performed at the end of the file, protecting the previous content to be
* overwritten. You can reposition (fseek, rewind) the internal pointer to

6
src/io/SDL_iostream.c
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@@ -94,10 +94,12 @@ static HANDLE SDLCALL windows_file_open(const char *filename, const char *mode)
// "r" = reading, file must exist
// "w" = writing, truncate existing, file may not exist
// "wx"= writing, file must not exist
// "r+"= reading or writing, file must exist
// "a" = writing, append file may not exist
// "a+"= append + read, file may not exist
// "w+" = read, write, truncate. file may not exist
// "w+x"= read, write, file must not exist
must_exist = (SDL_strchr(mode, 'r') != NULL) ? OPEN_EXISTING : 0;
truncate = (SDL_strchr(mode, 'w') != NULL) ? CREATE_ALWAYS : 0;
@@ -105,6 +107,10 @@ static HANDLE SDLCALL windows_file_open(const char *filename, const char *mode)
a_mode = (SDL_strchr(mode, 'a') != NULL) ? OPEN_ALWAYS : 0;
w_right = (a_mode || SDL_strchr(mode, '+') || truncate) ? GENERIC_WRITE : 0;
if (truncate && (SDL_strchr(mode, 'x') != NULL)) {
truncate = CREATE_NEW;
}
if (!r_right && !w_right) {
return INVALID_HANDLE_VALUE; // inconsistent mode
}

11
test/testautomation_iostream.c
View File

@@ -615,9 +615,9 @@ static int SDLCALL iostrm_testFileWrite(void *arg)
int result;
/* Write test. */
rw = SDL_IOFromFile(IOStreamWriteTestFilename, "w+");
SDLTest_AssertPass("Call to SDL_IOFromFile(..,\"w+\") succeeded");
SDLTest_AssertCheck(rw != NULL, "Verify opening file with SDL_IOFromFile in write mode does not return NULL");
rw = SDL_IOFromFile(IOStreamWriteTestFilename, "w+x");
SDLTest_AssertPass("Call to SDL_IOFromFile(..,\"w+x\") succeeded");
SDLTest_AssertCheck(rw != NULL, "Verify opening file with SDL_IOFromFile in exclusive write mode does not return NULL");
/* Bail out if NULL */
if (rw == NULL) {
@@ -632,6 +632,11 @@ static int SDLCALL iostrm_testFileWrite(void *arg)
SDLTest_AssertPass("Call to SDL_CloseIO() succeeded");
SDLTest_AssertCheck(result == true, "Verify result value is true; got: %d", result);
/* Exclusively opening an existing file should fail. */
rw = SDL_IOFromFile(IOStreamWriteTestFilename, "wx");
SDLTest_AssertPass("Call to SDL_IOFromFile(..,\"wx\") succeeded");
SDLTest_AssertCheck(rw == NULL, "Verify opening existing file with SDL_IOFromFile in exclusive write mode returns NULL");
return TEST_COMPLETED;
}