Example of Usage:

Example of Usage:

Example of Usage:

Example of usage:

Example of Usage:

Example of usage:

Examples of Usage:

Example of Usage:

The format string is comparable to the one provided in the "C" programming language. For most characters, printf simply prints the characters in the format string up to the terminating zero byte. The two exceptions are characters prefixed by a backslash ("\") and characters prefixed by a percent sign ("%"). Like C's printf, stdlib's printf uses the backslash as an escape character and the percent sign as a lead-in to a format string.

Printf uses the escape character ("\") to print special characters in a fashion similar to, but not identical to C's printf. Stdlib's printf routine supports the following special characters:

* r Print a carriage return (but no line feed)
* n Print a new line character (carriage return/line feed).
* b Print a backspace character.
* t Print a tab character.
* l Print a line feed character (but no carriage return).
* f Print a form feed character.
* \ Print the backslash character.
* % Print the percent sign character.
* 0xhh Print ASCII code hh, represented by two hex digits.

C users should note a couple of differences between stdlib's escape sequences and C's. First, use "\%" to print a percent sign within a format string, not "%%". C doesn't allow the use of "\%" because the C compiler processes "\%" at compile time (leaving a single "%" in the object code) whereas printf processes the format string at run-time. It would see a single "%" and treat it as a format lead-in character. Stdlib's printf, on the other hand, processes both the "\" and "%" and run-time, therefore it can distinguish "\%".

Strings of the form "\0xhh" must contain exactly two hex digits. The current printf routine isn't robust enough to handle sequences of the form "\0xh" which contain only a single hex digit. Keep this in mind if you find printf chopping off characters after you print a value.

There is absolutely no reason to use any escape character sequences except "\0x00". Printf grabs all characters following the call to printf up to the terminating zero byte (which is why you'd need to use "\0x00" if you want to print the null character, printf will not print such values). Stdlib's printf routine doesn't care how those characters got there. In particular, you are not limited to using a single string after the printf call. The following is perfectly legal:

printf
db	"This is a string",13,10
db	"This is on a new line",13,10
db	"Print a backspace at the end of this line:"
db	8,13,10,0

Your code will run a tiny amount faster if you avoid the use of the escape character sequences. More importantly, the escape character sequences take at least two bytes. You can encode most of them as a single byte by simply embedding the ASCII code for that byte directly into the code stream. Don't forget, you cannot embed a zero byte into the code stream. A zero byte terminates the format string. Instead, use the "\0x00" escape sequence.

Format sequences always between with "%". For each format sequence you must provide a far pointer to the associated data immediately following the format string, e.g.,

printf
db	"%i %i",0
dd	i,j

Format sequences take the general form "%s\cn^f" where:

*	"%" is always the "%" character. Use "\%" if you actually want to print a percent sign.
*	s is either nothing or a minus sign ("-").
*	"\c" is also optional, it may or may not appear in the format item. "c" represents any printable character.
*	"n" represents a string of 1 or more decimal digits.
*	"^" is just the caret (up-arrow) character.
*	"f" represents one of the format characters: i, d, x, h, u, c, s, ld, li, lx, or lu.

The "s", "\c", "n", and "^" items are optional, the "%" and "f" items must be present. Furthermore, the order of these items in the format item is very important. The "\c" entry, for example, cannot precede the "s" entry. Likewise, the "^" character, if present, must follow everything except the "f" character(s).

The format characters i, d, x, h, u, c, s, ld, li, lx, and lu control the output format for the data. The i and d format characters perform identical functions, they tell printf to print the following value as a 16-bit signed decimal integer. The x and h format characters instruct printf to print the specified value as a 16-bit or 8-bit hexadecimal value (respectively). If you specify u, printf prints the value as a 16-bit unsigned decimal integer. Using c tells printf to print the value as a single character. S tells printf that you're supplying the address of a zero-terminated character string, printf prints that string. The ld, li, lx, and lu entries are long (32-bit) versions of d/i, x, and u. The corresponding address points at a 32-bit value which printf will format and print to the standard output.

The following example demonstrates these format items:

printf
db	"I= %i, U= %u, HexC= %h, HexI= %x, C= %c, "
db	"S= %s",13,10
db	"L= %ld",13,10,0
dd	i,u,c,i,c,s,l

The number of far addresses (specified by operands to the "dd" pseudo-opcode) must match the number of "%" format items in the format string. Printf counts the number of "%" format items in the format string and skips over this many far addresses following the format string. If the number of items do not match, the return address for printf will be incorrect and the program will probably hang or otherwise malfunction. Likewise (as for the print routine), the format string must end with a zero byte. The addresses of the items following the format string must point directly at the memory locations where the specified data lies.

When used in the format above, printf always prints the values using the minimum number of print positions for each operand. If you want to specify a minimum field width, you can do so using the "n" format option. A format item of the format "%10d" prints a decimal integer using at least ten print positions. Likewise, "%16s" prints a string using at least 16 print positions. If the value to print requires more than the specified number of print positions, printf will use however many are necessary. If the value to print requires fewer, printf will always print the specified number, padding the value with blanks. Printf will print the value right justified in the print field (regardless of the data's type). If you want to print the value left justified in the output file, use the "-" format character as a prefix to the field width, e.g.,

printf
db	"%-17s",0
dd	string

In this example, printf prints the string using a 17 character long field with the string left justified in the output field. By default, printf blank fills the output field if the value to print requires fewer print positions than specified by the format item. The "\c" format item allows you to change the padding character. For example, to print a value, right justified, using "*" as the padding character you would use the format item "%\*10d". To print it left justified you would use the format item "%-\*10d". Note that the "-" must precede the "\*". This is a limitation of the current version of the software. The operands must appear in this order. Normally, the address(es) following the printf format string must be far pointers to the actual data to print. On occasion, especially when allocating storage on the heap (using malloc), you may not know (at assembly time) the address of the object you want to print. You may have only a pointer to the data you want to print. The "^" format option tells printf that the far pointer following the format string is the address of a pointer to the data rather than the address of the data itself. This option lets you access the data indirectly.

Examples of Usage: