A re-creation of the printf function in C. Function _printf(const char *format, ...) takes in a string and produces the output according to a format as described below. The function _printf() writes output to stdout, the standard output stream. It writes the output under the control of a format string that specifies how subsequent arguments (or arguments accessed via the variable-length argument facilities of stdarg(3)) are converted for output.
Upon successful return, these functions return the number of characters printed (excluding the null byte used to end output to strings).
The format string is a character string, beginning and ending in its initial shift state, if any. The format string is composed of zero or more directives:
- ordinary characters (not %), which are copied unchanged to the output stream;
- and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the character %, and ends with a conversion specifier. In between there may be (in this order) zero or more flags, an optional minimum field width, an optional precision and an optional length modifier. The arguments must correspond properly (after type promotion) with the conversion specifier.
A character that specifies the type of conversion to be applied. The conversion specifiers and their meanings are:
The int argument is converted to signed decimal notation. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is 1. When 0 is printed with an explicit precision 0, the output is empty.
The unsigned int argument is converted to unsigned octal (o), unsigned decimal (u), or unsigned hexadecimal (x and X) notation. The letters abcdef are used for x conversions; the letters ABCDEF are used for X conversions. The precision, if any, gives the minimum number of digits that must appear; if the converted value requires fewer digits, it is padded on the left with zeros. The default precision is 1. When 0 is printed with an explicit precision 0, the output is empty.
If no l modifier is present, the int argument is converted to an unsigned char, and the resulting character is written. If an l modifier is present, the wint_t (wide character) argument is converted to a multibyte sequence by a call to the wcrtomb(3) function, with a conversion state starting in the initial state, and the resulting multibyte string is written.
The const char * argument is expected to be a pointer to an array of character type (pointer to a string). Characters from the array are written up to (but not including) a terminating null byte ('\0'); if a precision is specified, no more than the number specified are written. If a precision is given, no null byte need be present; if the precision is not specified, or is greater than the size of the array, the array must contain a terminating null byte.
Prints the string. Non printable characters (0 < ASCII value < 32 or >= 127) are printed this way: \x, followed by the ASCII code value in hexadecimal (upper case - always 2 characters) For: _printf("%S\n", "Holberton\nSchool"); Output: Holberton\x0ASchool
The void * pointer argument is printed in hexadecimal (as if by %#x or %#lx).
Prints the reversed string
Prints the rot13'ed string
A '%' is written. No argument is converted. The complete conversion specification is '%%'.
- Code must comply with the Betty style and document checks.
- Compile code using flags:
-Wall,-Werror,-Wextra,-pedantic,-Wno-format - Cannot use global variables.
- Restricted to no more than 5 functions per file.
- Function prototypes should be included in header file
holberton.h - Header files should be include guarded.
- Authorized functions and macros:
write(man 2 write)malloc(man 3 malloc)free(man 3 free)va_start(man 3 va_start)va_end(man 3 va_end)va_copy(man 3 va_copy)va_arg(man 3 va_arg)
This piece of code shows that we have array of structs with specifiers and function pointers to the functions that copy argument related to specifier into the buffer.
At the end we print content of the buffer that holds output according to a format.
To learn how function pointers, variatic functions, pointers, structs etc. works.
Clone the project repo and compile it. It was compiled using this command: gcc -Wall -Wextra -Werror -pedantic -Wno-format main.c _putchar.c cpy_string.c cpy_int.c _printf.c cpy_special.c -o printf main.c is c program with test cases (look at example bellow).
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holberton.h - header file
- contains prototypes of all the functions described bellow
- definition of a struct used to define specifiers and functions that make a copy into the buffer
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_printf.c
- _printf - uses array of structs to find specifier and functions that would copy argument related to that specifier into the buffer and then prints out the content of the buffer at the end and returns the length of printed string.
- buffer_full - once buffer gets full it prints the content of that buffer to standard output and resets it to zero and returns index to 0
- clear_buffer - resets buffer to zeros
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cpy_int.c
- cpy_int - copies argument of type int into the buffer
- cpy_ui - copies argument of type unsigned int into the buffer
- cpy_hex - copies argument of type unsigned int converted to lower case hexadecimal into the buffer
- cpy_HEX - copies argument of type unsigned int converted to upper case hexadecimal into the buffer
- cpy_oct - copies argument of type unsigned int converted to octal into the buffer
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cpy_string.c
- cpy_string - copies argument of type char* (pointer to string) into the buffer - cpy_char - copies argument of type char into the buffer - cpy_rev - copies argument of type char* (pointer to string) in reverse into the buffer
- cpy_bin - copies argument of type unsigned int converted to binary into the buffer
- cpy_rot13 - copies argument of type char* (pointer to string) converted to rot13 into the buffer
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cpy_special.c
- cpy_special - prints the string where non printable characters (0 < ASCII value < 32 or >= 127) printed this way: \x, followed by the ASCII code value in hexadecimal (upper case - always 2 characters)
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_putchar.c
- _putchar - prints a character passed as argument to standard output
- _strlen - returns length of a string passed to it as argument
- _strprint - prints a string passed to it as argument to standard output
- _strcpy - copies one string into another
Example of a test program comparing system printf comapring to this project:
The output of the above test case:
Julija Lee and Galina Veratsennik
Project for Holberton School