The scanf placeholder consists of % at the beginning and a type indicator at the end. Apart from that it can have *, a maximum field-width indicator, and a type indicator modifier, for example,
%10.2f,%10d
d, i Used for signed integers; the expected argument should be a pointer to int.
o Used for unsigned int expected's value. It should be an integer in octal form.
U Unsigned integer in decimal form.
X, Unsigned integer in hexadecimal form.
E, f, g, G Floating-point values.
S Character string. It matches a sequence of non-whitespace characters terminated by an end-of-line or end-of-file character. The additional argument should be a pointer to char and should point to an area that is large enough to hold the input string as well as the NULL terminator.
C Matches the number of characters according to a specified field-width. If no width is specified then a single character is assumed. The additional argument must be a pointer to char; the area pointed to should be large enough to hold the specified number of characters.
N Does not read any input but writes the number of characters so far in the target variable.
The * is used to suppress input. For example, with %*d, if your input consists of 5 values and you want to ignore the middle 3 values, you can write:
scanf(" %d %*d %*d%*d %d ", &i, &j)
So, if your input is
10 20 30 40 50
it will get the value 10 and j will get the value 50. This is useful when you are getting the input from a file.
scanf requires two inputs: the first is a string argument and the second is a set of additional arguments.
You can define how the input is to be taken by using placeholders.
The general form of a placeholder is:
% flags field-width precision prefix type-identifier.
The type-identifiers are as follows:
d, i Signed integers
o Unsigned integers displayed in octal form.
u Unsigned integers in decimal form.
x Unsigned integers in hexadecimal form, and the hexadecimal characters a, b, c, d, e, and f printed in lowercase.
X Unsigned integer in hexadecimal form, and the hexadecimal characters A, B, C, D, E, and F printed in uppercase.
c Any value converted to unsigned char and displayed; c is used mainly for printing characters.
s The argument is converted to a character array and is printed; the last null in the string is not printed.
f Floating point.
e, E Floating point displayed in exponential form. It will have one digit to the left of the decimal point; the number of digits on the right side of the decimal point depends on the required precision.
g, G The value can be printed in floating point or exponential form. The exponential form is used if the exponent is less than –1 or if the exponent causes more places than required by the specified precision; the decimal point appears only if it is followed by a digit.
n This indicates to print the number of characters that are printed so far by printf.
p It indicates an additional argument pointer to void; the value of the pointer is converted to a sequence of characters.
h It can appear before type indicators d, i, o, u, x, and X. It indicates that the value to be displayed should be interpreted as short; for example, short integer (hd) and short unsigned integer (hu).
l It can appear before type-identifiers d, i, o, u, x, and X. It indicates that the value to be displayed should be interpreted as long; for example, long integer (hd) and long unsigned integer (hu).
l, L Available for type-identifiers e, E, f, g, and G. It indicates that a value should be indicated as long double.
Field-width indicates the least number of columns that will be allocated to the output. For example, if you write %4d to i and the value of i is 10, then 4 columns are allocated for i and 2 blank are added on left side of value of i. So the output is bb10. Here, b indicates blank.
If the value is more than the specified column, field-width is ignored and the number of columns used is equal to the number of columns required by the arguments. So if i is 12345 then 5 columns are used, even if %4d is specified.
In any circumstance, the output width is not shortened, because of field-width.
If you specify * instead of field-width then you have to specify additional arguments. For example,
printf ("%*d\n", 5, 20); // A
printf ("%*d\n", 20, 5); // B
In A, 5 is substituted for * and it indicates putting the value 20 in 5 columns.
In B, 20 is substituted for * and it indicates putting the value 5 in 20 columns.
Precision indicates the minimum number of digits printed for type integers d, i, o, u, x, and X. For example,
i. printf("%10.4d\n", 35)
Here 10 is the field-width and 4 is the precision, so 10 columns are used for the 4-digit output. To make 35 into 4 digits, two 0s are added to the left side to make it 0035. To print 0035 in 10 columns, blanks are added to make the output bbbbbb0035.
For floating arguments, precision indicates how many digits are printed after decimal points. If precision is more than the number of digits on the right side of the decimal point, 0s are added to the right side.
If precision indicates too few digits, then it is ignored and the number of digits are printed as necessary.
Flag characters are used to give directives for the output. You can use multiple flag characters in any order.
The flag characters are as follows:
— Indicates that output is left justified.
printf("%-10.4d\n", 25)
It causes the number to be printed as 0025bbbbbb. Thus, blanks are added to the right side.
+ Indicates that i number is printed using a sign character (+ or —).
printf("%+d\n", -25);
printf("%+d\n", 25);
It causes printing as
-25
+25
printf("% d\n", 25);
printf("% d", 25);
It causes printing in the form of
b25
25
In the first case, blank is displayed.
− # Indicates that the value should be converted to another form before displaying. For example, for hexadecimal values you can indicate 0X; for the floating data type, # indicates that the decimal point should always be included in the output.
0 Used with whole and real numbers, 0 causes 0s to be padded to complete the field width. If the precision is specified as 0, then this flag is ignored; if the 0 and – flags are both specified, the 0 flag is ignored.
Escape sequences are the special directives used to format printing. For example, \n indicates that the next printing should start from the first column of the next line. Following are the escape sequences:
\a Alert
Produces a beep or flash; the cursor position is not changed.
\b Backspace
Moves the cursor to the last column of the previous line.
\f Form feed
Moves the cursor to start of next page.
\n New line
Moves the cursor to the first column of the next line.
Moves the cursor to the first column of the current line.
\t Horizontal Tab
Moves the cursor to the next horizontal tab stop on the line.
\v Vertical Tab
Moves the cursor to the next vertical tab stop on the line.
\\
Prints \\.
\"
Prints "
%%
Prints %.
http://lxr.free-electrons.com/source/| () [] . -> ++ -- | Parentheses (function call) Brackets (array subscript) Member selection via object name Member selection via pointer Postfix increment/decrement | left-to-right |
| ++ -- + - ! ~ (type) * & sizeof | Prefix increment/decrement Unary plus/minus Logical negation/bitwise complement Cast (change type) Dereference Address Determine size in bytes | right-to-left |
| * / % | Multiplication/division/modulus | left-to-right |
| + - | Addition/subtraction | left-to-right |
| << >> | Bitwise shift left, Bitwise shift right | left-to-right |
| < <= > >= | Relational less than/less than or equal to Relational greater than/greater than or equal to | left-to-right |
| == != | Relational is equal to/is not equal to | left-to-right |
| & | Bitwise AND | left-to-right |
| ^ | Bitwise exclusive OR | left-to-right |
| | | Bitwise inclusive OR | left-to-right |
| && | Logical AND | left-to-right |
| || | Logical OR | left-to-right |
| ?: | Ternary conditional | right-to-left |
| = += -= *= /= %= &= ^= |= <<= >>= | Assignment Addition/subtraction assignment Multiplication/division assignment Modulus/bitwise AND assignment Bitwise exclusive/inclusive OR assignment Bitwise shift left/right assignment | right-to-left |
| , | Comma (separate expressions) | left-to-right |