The printf project is a collaboration between nora jeout and charifa masbahi, actual students of Software Engineering at alx africa, were a function named "_printf" imitates the actual "printf" command located in the stdio.h library. It contains some of the basic features and functions found in the manual 3 of "printf".
_printf() is a function that performs formatted output conversion and print data. Its prototype is the following:
int _printf(const char *format, ...)
Where format contains the string that is printed. As _printf() is variadic function, it can receives n arguments that replace by n tags written inside the string.
The format tags prototype is the following:
%[flags][length]specifier
- What is Variadic Functions?
Variadic function takes indefinite size arity and a variable number of arguments as a parameter. Situations that you do not know how many parameters pass the function.
- what is ellipses (...)?
The ellipsis (...) is part of the C language and indicates that there are 0 or more optional arguments.
- What is va_list?
a complete object type suitable for holding the information needed by the macros va_start, va_copy, va_arg, and va_end
- What is va_start?
gets the address of the first argument.
- What is va_arg?
dereference the block address and type cast it to the appropriate type. then goes to the next block of memory. What is a "Type Descriptor"?
- What is va_end?
performs cleanup for an ap object initialized by a call to va_start or va_copy
The printf function supports a wide range of format specifiers that allow for the formatting of output in a variety of ways. Here are the format specifiers that are supported in this implementation of printf:
If the program runs successfully, the return value is the amount of chars printed.
| Specifier | Output |
|---|---|
| c | Character |
| d or i | Signed decimal integer |
| s | String of characters |
| b | Signed binary |
| o | Signed octal |
| u | Unsigned integer |
| x | Unsigned hexadecimal |
| X | Unsigned hexadecimal (uppercase) |
| p | Pointer address |
| r | Reverse string of characters |
| R | ROT13 translation of string |
| S | String with special chars replaced by their ASCII value |
| % | Character |
| Flags | Description | Specifiers |
|---|---|---|
| + | Prints a plus sign (+) when the argument is a positive number. In other case, prints a minus sign (-). | i, d |
| (space) | Prints a blank space if the argument is a positive number | i, d |
| # | Prints 0, 0x and 0X for o, x and X specifiers, respectively. It doesn't print anything if the argument is zero | o, x, X |
| Length | Description | Specifiers |
|---|---|---|
| l | Prints a long int or unsigned long int | i, d, o, u, x and X |
| h | Prints a short int or unsigned short int | i, d, o, u, x and X |
To create our custom printf function, We need to plan out how it will work. We can create a flowchart to help us visualize the logic of the function. Here is an example of a simple flowchart for printf:
- start -> read format string -> while format string not empty ->
- parse next format specifier -> output text before specifier ->
- if specifier is %d -> output decimal number
- if specifier is %s -> output string
- if specifier is %c -> output character
- if specifier is %% -> output %
- if specifier is unknown -> output error
- end loop -> output remaining text -> end
