An alternate implementation of stdio that brings Linux goodies and fixes to Windows. At the moment, only mingw is supported for windows and gcc for linux.
The main reason I implemented this is because tmpfile() was broken on Windows with Windows Vista, and the workaround is excruciatingly bad performance. I need something like tmpfile() in order to implement open-output-string in my lisp runtime. It came to a head when porting a little slither.io clone I wrote to windows, and seeing the debug text routine taking an average of 10 miliseconds with frequent catastrophic stutters.
Truly one of the wackiest yak shaves I've done yet.
The killer feature of DFILE is the d_fopencookie() function, which is like the glibc function, except you can use it on windows!
And I needed it to implement the d_strfile() function, which returns a DFILE stream, just as tmpfile() returns a FILE stream. Except d_strfile() does not write to a real tempfile, but instead flushes to an unrolled linked list of pages 4096 chars long.
In addition, d_tmpfile() is also not broken on Windows (though as noted above, it is catastrophically slow), and DFILEs use unix style line endings for everything. So, d_fseek() is not broken, there is no need for binary file modes, and ugly carriage returns don't infect your files. Likewise, DFILE doesn't use locales, so no random chaos happening upon print or scan. For localization, stdio is the incorrect choice anyway.
Replace FILE* with DFILE* throughout your code. All dfile functions and variables have the same as stdio, just prefixed with d_. So d_puts("Hello, world!", d_stdout).
Most of the function calls are the same: the only major difference is d_fread_unlocked and d_fwrite_unlocked, which have the simplified interface. Also, d_ftell and d_fseek use off64_t instead of off_t, so that isn't broken on windows. Definitions of off64_t and ssize_t are provided.
int d_fread_unlocked(void * ptr, int ct, DFILE * f);
int d_fwrite_unlocked(void * ptr, int ct, DFILE * f);
The d_ungetc function supports the minimum necessary to implement scanf wthout flushing at the end and be posix compliant, 2 ungets.
Bonus: d_fmemopen accepts a '0' flag which causes it to ignore writes and read 0s past the end of a buffer, similar to "robust buffer access" on desktop GPUs. For example:
char buf[5];
DFILE * f = d_fmemopen(buf, sizeof buf, "w0+");
char * msg = "Hello, Dweebs!";
int nchars = d_fwrite_unlocked(msg, strlen(msg), f);
// writes Hello to the buffer, but reports 14 chars written.
char buf2[32];
d_fseek(f, 0, SEEK_SET);
nchars = d_fread_unlocked(buf2, sizeof buf2, f);
// reads 32 chars into buf2, reading Hello\0\0\0\0...
This may be how snprintf is implemented :)
Further bonuses: the mode strings have additional flags: l for opening a file immediately in line buffered mode, and likewise u for unbuffered mode (d_fmemopen ignores these flags and always opens unbuffered)
NOTE: dfile only flushes line buffered output when the buffer of line buffered input is populated. Unbuffered reads do not flush output.
Also, dfile relies on termios for line buffered input. line buffered input will act fully buffered on non-terminals and improperly configured terminals.
dfile implements double printing via dragonbox and double parsing via fast_float.
Things my yak shave didn't require
- printf custom formatter: something I desire, something others have requested
- performance lol: no optimization work has been done, have been focused on correctness
Notably, d_printf supports wN and wfN formats. Free from PRIu64 at last.
d_printf also adds a 'roundtrip' flag, which always prints enough floating point digits to roundtrip the number. When roundtrip is set, the precision defaults to 0 instead of 6. Example usage: d_printf("%rf %rf\n", 0.3, 0.1 + 0.2); and d_printf("%r.6f\n", 0.3);
| format | + | - | # | space | 0 | r | width | precision | size |
|---|---|---|---|---|---|---|---|---|---|
| d | yes | yes | - | yes | yes | - | yes | yes | yes |
| u | - | yes | - | - | yes | - | yes | yes | yes |
| x | - | yes | yes | - | yes | - | yes | yes | yes |
| o | - | yes | yes | - | yes | - | yes | yes | yes |
| b | - | yes | yes | - | yes | - | yes | yes | yes |
| f | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| g | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| a | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| e | yes | yes | yes | yes | yes | yes | yes | yes | yes |
| c | - | yes | - | - | - | - | yes | - | no |
| s | - | yes | - | - | - | - | yes | - | no |
| m | - | yes | - | - | - | - | yes | - | - |
| p | - | yes | - | - | - | - | yes | yes | - |
| n | - | - | - | - | - | - | - | - | yes |
Widechar strings are not supported because a basic implementation would invite locales, and I'm not ready for an advanced implementation.
| format | * | width | size |
|---|---|---|---|
| d | yes | yes | yes |
| u | yes | yes | yes |
| x | yes | yes | yes |
| o | yes | yes | yes |
| b | yes | yes | yes |
| gfae | yes | yes | yes |
| c | yes | yes | no |
| s | yes | yes | no |
| [ | yes | yes | no |
| p | yes | yes | - |
| n | - | - | yes |