Add D3_(v)snprintfC99() for C99-compatible implementations

These are now used by idStr::(v)snPrintf(), and in the future can
be used if a (v)snprintf() that's guaranteed not to call
common->Warning() or similar is needed (e.g. used during early startup)

idlib/Str.cpp

@@ -30,6 +30,7 @@ If you have questions concerning this license or the applicable additional terms
 #include "idlib/math/Vector.h"
 #include "idlib/Heap.h"
 #include "framework/Common.h"
+#include <limits.h>
 
 #include "idlib/Str.h"
 
@@ -1513,21 +1514,25 @@ idStr::snPrintf
 ================
 */
 int idStr::snPrintf( char *dest, int size, const char *fmt, ...) {
-	int len;
 	va_list argptr;
-	char buffer[32000];	// big, but small enough to fit in PPC stack
-
+	int len;
 	va_start( argptr, fmt );
-	len = vsprintf( buffer, fmt, argptr );
+	len = D3_vsnprintfC99(dest, size, fmt, argptr);
 	va_end( argptr );
-	if ( len >= sizeof( buffer ) ) {
+	if ( len >= 32000 ) {
+		// TODO: Previously this function used a 32000 byte buffer to write into
+		//       with vsprintf(), and raised this error if that was overflowed
+		//       (more likely that'd have lead to a crash..).
+		//       Technically we don't have that restriction anymore, so I'm unsure
+		//       if this error should really still be raised to preserve
+		//       the old intended behavior, maybe for compat with mod DLLs using
+		//       the old version of the function or something?
 		idLib::common->Error( "idStr::snPrintf: overflowed buffer" );
 	}
 	if ( len >= size ) {
 		idLib::common->Warning( "idStr::snPrintf: overflow of %i in %i\n", len, size );
 		len = size;
 	}
-	idStr::Copynz( dest, buffer, size );
 	return len;
 }
 
@@ -1550,18 +1555,7 @@ or returns -1 on failure or if the buffer would be overflowed.
 ============
 */
 int idStr::vsnPrintf( char *dest, int size, const char *fmt, va_list argptr ) {
-	int ret;
-
-#ifdef _WIN32
-#undef _vsnprintf
-	ret = _vsnprintf( dest, size-1, fmt, argptr );
-#define _vsnprintf	use_idStr_vsnPrintf
-#else
-#undef vsnprintf
-	ret = vsnprintf( dest, size, fmt, argptr );
-#define vsnprintf	use_idStr_vsnPrintf
-#endif
-	dest[size-1] = '\0';
+	int ret = D3_vsnprintfC99(dest, size, fmt, argptr);
 	if ( ret < 0 || ret >= size ) {
 		return -1;
 	}
@@ -1790,3 +1784,57 @@ idStr idStr::FormatNumber( int number ) {
 
 	return string;
 }
+
+// behaves like C99's vsnprintf() by returning the amount of bytes that
+// *would* have been written into a big enough buffer, even if that's > size
+// unlike idStr::vsnPrintf() which returns -1 in that case
+int D3_vsnprintfC99(char *dst, size_t size, const char *format, va_list ap)
+{
+	// before VS2015, it didn't have a standards-conforming (v)snprintf()-implementation
+	// same might be true for other windows compilers if they use old CRT versions, like MinGW does
+#if defined(_WIN32) && (!defined(_MSC_VER) || _MSC_VER < 1900)
+  #undef _vsnprintf
+	// based on DG_vsnprintf() from https://github.com/DanielGibson/Snippets/blob/master/DG_misc.h
+	int ret = -1;
+	if(dst != NULL && size > 0)
+	{
+#if defined(_MSC_VER) && _MSC_VER >= 1400
+		// I think MSVC2005 introduced _vsnprintf_s().
+		// this shuts up _vsnprintf() security/deprecation warnings.
+		ret = _vsnprintf_s(dst, size, _TRUNCATE, format, ap);
+#else
+		ret = _vsnprintf(dst, size, format, ap);
+		dst[size-1] = '\0'; // ensure '\0'-termination
+#endif
+	}
+
+	if(ret == -1)
+	{
+		// _vsnprintf() returns -1 if the output is truncated
+		// it's also -1 if dst or size were NULL/0, so the user didn't want to write
+		// we want to return the number of characters that would've been
+		// needed, though.. fortunately _vscprintf() calculates that.
+		ret = _vscprintf(format, ap);
+	}
+	return ret;
+  #define _vsnprintf	use_idStr_vsnPrintf
+#else // other operating systems and VisualC++ >= 2015 should have a proper vsnprintf()
+  #undef vsnprintf
+	return vsnprintf(dst, size, format, ap);
+  #define vsnprintf	use_idStr_vsnPrintf
+#endif
+}
+
+// behaves like C99's snprintf() by returning the amount of bytes that
+// *would* have been written into a big enough buffer, even if that's > size
+// unlike idStr::snPrintf() which returns the written bytes in that case
+// and also calls common->Warning() in case of overflows
+int D3_snprintfC99(char *dst, size_t size, const char *format, ...)
+{
+	int ret = 0;
+	va_list argptr;
+	va_start( argptr, format );
+	ret = D3_vsnprintfC99(dst, size, format, argptr);
+	va_end( argptr );
+	return ret;
+}

idlib/Str.h

@@ -1068,4 +1068,15 @@ ID_INLINE int idStr::DynamicMemoryUsed() const {
 	return ( data == baseBuffer ) ? 0 : alloced;
 }
 
+// behaves like C99's snprintf() by returning the amount of bytes that
+// *would* have been written into a big enough buffer, even if that's > size
+// unlike idStr::snPrintf() which returns the written bytes in that case
+// and also calls common->Warning() in case of overflows
+int D3_snprintfC99(char *dst, size_t size, const char *format, ...) id_attribute((format(printf,3,4)));
+
+// behaves like C99's vsnprintf() by returning the amount of bytes that
+// *would* have been written into a big enough buffer, even if that's > size
+// unlike idStr::vsnPrintf() which returns -1 in that case
+int D3_vsnprintfC99(char *dst, size_t size, const char *format, va_list ap);
+
 #endif /* !__STR_H__ */