[flac-dev] vsnprintf_s and vsnprintf

[Erik de Castro Lopo]

lvqcl wrote:

> I wrote a small program that fills a buffer[] with "abcdefghijklmnopqrstuvwxyz\0"
> pattern and then tries to write "0123456789" string into it.
> It calls either
> 	ret = vsnprintf_s(buffer, buf_size, _TRUNCATE, fmt, va);
> or
> 	ret = vsnprintf(buffer, buf_size, fmt, va);

<snip>

>   vsnprintf (MSVC, MinGW):
> 
>   buf_size = 8;        ret = -1;        buffer = "01234567ijklmnopqrstuvwxyz"
>   buf_size = 9;        ret = -1;        buffer = "012345678jklmnopqrstuvwxyz"
>   buf_size = 10;       ret = 10;        buffer = "0123456789klmnopqrstuvwxyz"
>   buf_size = 11;       ret = 10;        buffer = "0123456789"
>   buf_size = 12;       ret = 10;        buffer = "0123456789"

This is actually the only one we can use.

With a check on the the return value and a line or two of extra
code, this function can made to behave resonably sensibly, even it
its not possible to make it meet the requirements if the ISO C specs.

I'm basically think of something like the (untested) diff below.

Erik



diff --git a/src/share/grabbag/snprintf.c b/src/share/grabbag/snprintf.c
index 3a0661f..6a4e3ea 100644
--- a/src/share/grabbag/snprintf.c
+++ b/src/share/grabbag/snprintf.c
@@ -62,8 +62,11 @@ flac_snprintf(char *str, size_t size, const char *fmt, ...)
        va_start (va, fmt);
 
 #ifdef _MSC_VER
-       rc = vsnprintf_s (str, size, _TRUNCATE, fmt, va);
-       rc = (rc > 0) ? rc : (size == 0 ? 1024 : size * 2);
+       rc = vsnprintf (str, size, fmt, va);
+       if (rc < 0) {
+               rc = size - 1;
+               str [rc] = 0;
+       }
 #else
        rc = vsnprintf (str, size, fmt, va);
 #endif

-- 
----------------------------------------------------------------------
Erik de Castro Lopo
http://www.mega-nerd.com/