ft_printf

Are you tired of using alternatively ft_putstr and ft_putnbr for your displays? You don’t have the right to use printf? Re-code your own! This is a good time to discover a C feature: variadic functions, and to train your display options management skills. You will then be able to use your ft_printf in all future projects.

This was the first project in the algorithms branch (old curriculum).

Conversion Specifications

A conversion specification is made up of the following parts:

%[flags][min-field-width].[precision][length]Specifier

Flags

These are the flags to implement:

• #: Alternate form

• 0: Zero padded (ignored if '-' flag, or specified 'Precision' with d i o u x X)

• -: Left align result

• +: Prepend sign (+ or -) to SIGNED conversions

• : (A space character. Overrides '+' flag) Leave a space before:

  • Positive numbers produced by SIGNED conversions.
  • Before strings.

Length

The length modifier:

• h: Signed/unsigned char: hd, hi, hu

  1. Signed: hd, hi
  2. Unsigned: hu

• hh: Signed/unsigned short int: hhc, hhu

  1. Signed: hhc
  2. Unsigned: hhu

• l: Signed/unsigned long int:

  1. Signed: ld, li, l
  2. Unsigned: lu

• ll: Signed/unsigned long long int: lld, lli, llu Signed double: llf, lli, llu

• L: Signed long double: Lf

Specifiers

The specifier is the last part of a conversion specification. These are the ones we had to implement:

• c: character
• s: string
• d: integer
• i: integer
• u: unsigned integer
• p: memory address (0x7ffc48)
• x: hexadecimal (7ffc48)
• X: hexadecimal (7FFC48)
• f: float (always signed in C)

Error messsages?

Since we were supposed to create a non buffered version of printf, I didn't do any error handling. But these are the type of error and error messages I was considering at the beginning:

• When there are more data arguments than conversion specifiers:

printf("hello %d\n", 3, 3);

error: data argument not used by format string

• When there are more conversion specifiers than data arguments:

printf("hello %d %d\n", 3);

error: more '%' conversions than data arguments

• When the specifier doesn't match the data argument:

printf("hello %d\n", 3.3);

error: format specifies type 'int' but the argument has type 'double'

• When we use conversion specification w/o conversion specifiers: // printf(" test percent: %"); // error: incomplete format specifier // printf(" test percent: % \n"); // error: invalid conversion specifier '\x0a'

Valgrind: checking for leaks

1. Compile your program with the -g option.

2. Run:

valgrind --leak-check=yes --log-file=/tmp/test_printf.log ./test_printf -s

3. Check logs:

cat /tmp/test_printf.log

Extensibility

Once a new function is added to the dispatcher, don't forget to update the length of the FUN macro, used to allocate memory for the array of function pointers by 'init_dispatcher' (in ft_printf.c).