In the most simple case, printf takes one argument: a string of characters to be printed. This string is composed of characters, each of which is printed exactly as it appears. So printf("xyz"); would simply print an x, then a y, and finally a z.
To identify the start of the string, we put a doublequote (") at the front. To identify the end of the string we put another double-quote at the end. But what if we want to actually print a double-quote? We can’t exactly put a double-quote in the middle of the string because it would be mistaken for the end-of-string marker. Double-quote is a special char- acter. The normal print-what-you-see rules do not apply.
| Character | Escaped Character |
|---|---|
| \ | \\ |
| " | \" |
| ' | \' |
| % | \% |
| newline | \n |
| tab | \t |
| Null byte | \0 |
On the other hand we have characters that normally print as you would expect, but when you add a backslash, then they become special. An example is the newline character. To print an n, we simply type in an n. To print a newline, we type in a \n, thus invoking the alternate meaning of n, which is newline.
| Character | Description |
|---|---|
| \a | audible alert (bell) |
| \b | backspace |
| \f | form feed |
| \n | newline (linefeed) |
| \r | carriage return |
| \t | tab |
| \v | vertical tab |
The real power of printf is when we are printing the contents of variables. Let’s take the format specifier %d for example. This prints a number. So, a number must be provided for printing. This is done by adding another argument to the printf statement, as shown here.
int age;
age = 25;
printf ( "I am %d years old\n", age );
In this example, printf has two arguments. The first is a string: "I am %d years old\n". The second is an integer, age.
When an argument is to be printed by printf, there must be an percentage sign % preceeding the format specifier, modifiers (flags, field width, precision, and length modifiers).
- Flags: Control the alignment and representation of the output (e.g., %-10d for left-justified integer).
- Field Width: Specify the minimum width of the output field (e.g., %5d for a minimum width of 5 characters).
- Precision: Control the number of decimal places for floating-point numbers (e.g., %.2f for two decimal places).
- Length Modifiers: Specify the size of the argument (e.g., %ld for a long integer).
- %c: prints a character
- %s: prints a string
- %%: prints a percent sign
% - %d: prints a decimal (base 10) number
- %i: prints an integer number
- %b: prints a binary number from an unsigned int
- %u: prints an unsigned int
- %o: prints an octal number from an unsigned int
- %x: prints a hexadecimal number in lower case from an unsigned int
- %X: prints a hexadecimal number in upper case from an unsigned int
- %S: prints a string while converting any Non printable characters (0 < ASCII value < 32 or >= 127) in this way: \x, followed by the ASCII code value in hexadecimal (upper case - always 2 characters)
- %p: prints an address
- %r: prints a string in reverse
- %R: prints the rot13'ed string
-: Left-justify the result within the field width. It is right justified by default.+: Prefix the output value with a sign (+ or -) if the output value is of a signed type. Only negative sign appears by default.space ' ': Prefix the output value with a blank if the output value is signed and positive. The + flag overrides the blank flag if both appear, and a positive signed value will be output with a sign.#: It behaves differently depending on which specifier it is paired with:- When used with the o, x, or X formats, the # flag prefixes any nonzero output value with 0, 0x, or 0X, respectively.
- When used with the p format, the # flag converts the pointer to hex digits. These hex digits cannot be converted back into a pointer, unless in a teraspace environment.
- th
#flag should not be used with c, lc, d, i, u, or s types.
0: When used with the d, i, D(n,p) o, u, x, or X, the 0 flag causes leading 0s to pad the output to the field width. The 0 flag is ignored if precision is specified for an integer or if the - flag is specified.