_printf()

Prints text to terminal based on a given format string to standard output. Mimicking glibc printf.

Syntax: _printf(<format string>, args...)

Current features

Implemented specifiers:

Decimal integers (%d)
Unsigned decimal integers (%u)
Strings (%s)
Hex integers (%x %X)
Octal integers (%o)
Binary integers (%b)
Pointer notation for integers (%p)
Print a string, but print hidden characters as hex codes (%S)
Reversed strings (%r)
Rot13'd strings (%R)

Implemented flags and options:

Width
Precision
+/space to set sign
- to left justify
# to display hex/octal binary prefix
* and .* to accept variables for width and precision
hh, h, and l length flags

Getting started

The simplest way to add this to your project would be to compile the whole codebase with your project. Likely you'll want to compile and include it as a static library to avoid logistical hassles though. To do so for a single project using gcc run these commands from the root printf directory:

gcc -c \*.c
ar rcs libprintf.a \*.o

After this, copy the resulting printf.a file and printf.h to your project directory. Include printf.h where appropriate in your source files. Then using GCC as an example, when compiling add the -l flag with the library file name like so:

gcc <your stuff here> libprintf.a

Usage Examples

The simplest example is just printing out a string literal as the format string, like so:

_printf("Hello printf!");

This will output the text "Hello printf!" to the terminal, like so:

Hello printf!

Rountinely, you will want to use printf to print out strings from variables or numbers. We can take in variables passed as further arguments by using %, then flags (optional), then a specifier for the type of thing we are printing. If we have an integer and a string, we will use %d and %s respectively, like so:

char str[] = "world";
int number = 42;
_printf("Hello %s %d!", str, number);

We will get the output:

Hello world 42!

Printf takes the specifiers in the order they appear in the format string, so in this case our string variable must be before our integer variable, or else printf will try printing the string like an integer and vice versa, would could cause a crash! There are various options to change how and where the text is output which can be combined together, and a complete readable listing can be found at http://www.cplusplus.com/reference/cstdio/printf/

There are a few non-standard specifiers in this version of printf. One is %S, which prints normally invisible characters as hex codes. Like so:

char str[]="\x14<-I can see you->\x15";
_printf("%S", str);

When this is run we should get:

\x14<-I can see you->\x15

There is a specifiers to print a string in reverse (%S):

char str[] = "SdrakcaB";
_printf(%r,str);

Will net us:

BackwardS

The rot13 specifier (%R) will shift all characters 13 letters forward, turning every "a" into an "n" and so on. Finally, there is a binary number specifier (%b):

int number = 19;
_printf("%b", number);

This should get us the binary number output:

Testing

The tests folder includes a mains.c file which will run a series of pairs of printf statements on many different combinations of specifiers, flag and options using both this version of print and stdlib printf, and output this to stdout. To run these tests, compile the entire project then run the resulting executable:

gcc -o printftest *.c tests/mains.c
./printftest

Authors