#include <cstdio> int printf( const char *format, ... );
The printf() function prints output to stdout, according to format and other arguments passed to printf(). The string format consists of two types of items - characters that will be printed to the screen, and format commands that define how the other arguments to printf() are displayed. Basically, you specify a format string that has text in it, as well as "special" characters that map to the other arguments of printf(). For example, this code
char name = "Bob"; int age = 21; printf( "Hello %s, you are %d years old\n", name, age );
displays the following output:
Hello Bob, you are 21 years old
The %s means, "insert the first argument, a string, right here." The %d indicates that the second argument (an integer) should be placed there. There are different %-codes for different variable types, as well as options to limit the length of the variables and whatnot.
An integer placed between a % sign and the format command acts as a minimum field width specifier, and pads the output with spaces or zeros to make it long enough. If you want to pad with zeros, place a zero before the minimum field width specifier:
You can also include a precision modifier, in the form of a .N where N is some number, before the format command:
The precision modifier has different meanings depending on the format command being used:
All of printf()'s output is right-justified, unless you place a minus sign right after the % sign. For example,
will display a floating point number with a minimum of 12 characters, 4 decimal places, and left justified. You may modify the %d, %i, %o, %u, and %x type specifiers with the letter l and the letter h to specify long and short data types (e.g. %hd means a short integer). The %e, %f, and %g type specifiers can have the letter l before them to indicate that a double follows. The %g, %f, and %e type specifiers can be preceded with the character '#' to ensure that the decimal point will be present, even if there are no decimal digits. The use of the '#' character with the %x type specifier indicates that the hexidecimal number should be printed with the '0x' prefix. The use of the '#' character with the %o type specifier indicates that the octal value should be displayed with a 0 prefix.
Inserting a plus sign '+' into the type specifier will force positive values to be preceded by a '+' sign. Putting a space character ' ' there will force positive values to be preceded by a single space character.
You can also include constant escape sequences in the output string.
The return value of printf() is the number of characters printed, or a negative number if an error occurred.