VFPrintf

format and print a string to a file (buffered) (V36)

Writes the formatted string and values to the given file. This function is assumed to handle all internal buffering so that the formatting string and resultant formatted values can be arbitrarily long. Any secondary error code is returned in IoErr(). This operation is buffered.

fh

Filehandle to write to

fmt

RawDoFmt() style formatting string

argv

Pointer to array of formatting values

count

Number of bytes written or -1 (EOF) for an error; call IoErr() to find out why VFPrintf()/FPrintf() has failed.

The "locale.library" (introduced with Workbench 2.1) will install its own replacement sprintf()-like formatting code via SetFunction(). This replacement has significantly higher stack size requirements than the original exec.library version of RawDoFmt(). You are best advised to only call RawDoFmt(), even indirectly such as through the dos.library/VFPrintf function, if there are more than 1000 bytes of stack space available. The stack size requirements apply to all locale.library versions up to and including V46.8 (AmigaOS 3.1.4), which all default to prepare for positional arguments such as "%2$s", regardless of whether these are used in the format specification string. Starting with locale.library V47.26 (AmigaOS 3.2) will prepare for positional arguments only if the format specification string calls for it. As a general precaution, you should always assume that preparations for positional arguments are being made.

The exec.library/RawDoFmt() function provides only a limited set of format conversion operations, with the available choices covering what the 1978 first edition of "The 'C' Programming Language" would describe. Printf() and VPrintf() only support the "%d", "%x", "%u", "%c" and "%s" conversions, as well as the "%ld", "%lx", "%lu" and "%lc" conversion variants. Floating point number conversion is not supported, and neither is conversion of integer values into octal format.

Printf() and VPrintf() are only suitable for those cases in which its limited feature set is not an issue. You may want to consider using your 'C' compiler's sprintf/vsprintf/printf/vprintf library functions instead.

Should you opt for Printf() and VPrintf() you must be careful not to get tripped up by the default behaviour of the RawDoFmt() function in assuming that "%d", "%x", "%u", "%c" parameters are 16 bits in size. In terms of C99 (ISO/IEC 9899:1999) RawDoFmt() treats "%d" like "%hd", "%x" like "%hx", etc. and it treats "%c" like "%hc".

For these reasons, you should verify that the format specification you use with Printf() and VPrintf() does not apply "%d", "%x", "%u" and "%c" indiscriminately. Amiga 'C' compilers default to using 32 bit integers as parameters to varargs functions such as Printf(). You would use the "%ld", "%lx", "%lu" and "%lc" rather than the "%d", "%x", "%u" "%c" forms. You will notice that the wrong format specification will invariably produce unexpected behaviour, such as garbled output and invalid memory accesses.

The V40 function prototype for FPrintf() forced you to cast the first varargs parameter to LONG due to a deficiency in the program that generates fd files, prototypes, and amiga.lib stubs. This was fixed in V44.

VPrintf(), VFWritef(), FPutC(), exec.library/RawDoFmt, locale.library/FormatString