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scanf Type Field Characters

The following information applies to any of the scanf family of functions, including the secure versions, such as scanf_s.

The type character is the only required format field; it appears after any optional format fields. The type character determines whether the associated argument is interpreted as a character, string, or number.

Type Characters for scanf functions
Character Type of input expected Type of argument Size argument in secure version?

c

Character. When used with scanf functions, specifies single-byte character; when used with wscanf functions, specifies wide character. White-space characters that are ordinarily skipped are read when c is specified. To read next non–white-space single-byte character, use %1s; to read next non–white-space wide character, use %1ws.

Pointer to char when used with scanf functions, pointer to wchar_t when used with wscanf functions.

Required. Size does not include space for a null terminator.

C

Opposite size character. When used with scanf functions, specifies wide character; when used with wscanf functions, specifies single-byte character. White-space characters that are ordinarily skipped are read when C is specified. To read next non–white-space single-byte character, use %1s; to read next non–white-space wide character, use %1ws.

Pointer to wchar_t when used with scanf functions, pointer to char when used with wscanf functions.

Required. Size argument does not include space for a null terminator.

d

Decimal integer.

Pointer to int.

No.

i

Decimal, hexadecimal, or octal integer.

Pointer to int.

No.

o

Octal integer.

Pointer to int.

No.

u

Unsigned decimal integer.

Pointer to unsigned int.

No.

x

Hexadecimal integer.

Pointer to int.

No.

e, E, f, g, G

Floating-point value consisting of optional sign (+ or –), series of one or more decimal digits containing decimal point, and optional exponent ("e" or "E") followed by an optionally signed integer value.

Pointer to float.

No.

n

No input read from stream or buffer.

Pointer to int, into which is stored number of characters successfully read from stream or buffer up to that point in current call to scanf functions or wscanf functions.

No.

s

String, up to first white-space character (space, tab or newline). To read strings not delimited by space characters, use set of square brackets ([ ]), as discussed in scanf Width Specification.

When used with scanf functions, signifies single-byte character array; when used with wscanf functions, signifies wide-character array. In either case, character array must be large enough for input field plus terminating null character, which is automatically appended.

Required. Size includes space for a null terminator.

S

Opposite-size character string, up to first white-space character (space, tab or newline). To read strings not delimited by space characters, use set of square brackets ([ ]), as discussed in scanf Width Specification.

When used with scanf functions, signifies wide-character array; when used with wscanf functions, signifies single-byte–character array. In either case, character array must be large enough for input field plus terminating null character, which is automatically appended.

Required. Size includes space for a null terminator.

The a and A specifiers (see printf Type Field Characters) are not available with scanf.

The size arguments, if required, should be passed in the parameter list immediately following the argument they apply to. For example, the following code:

char string1[11], string2[9];
scanf("%10s %8s", string1, 11, string2, 9);

reads a single character into c, a decimal integer into i, a string with a maximum length of 10 into string1, and a string with a maximum length of 8 into string2. The buffer sizes should be at least one more than the width specifications since space must be reserved for the null terminator.

The format string can handle single-byte or wide character input regardless of whether the single-byte character or wide-character version of the function is used. Thus, to read single-byte or wide characters with scanf functions and wscanf functions, use format specifiers as follows.

To read character as Use this function With these format specifiers

single byte

scanf functions

c, hc, or hC

single byte

wscanf functions

C, hc, or hC

wide

wscanf functions

c, lc, or lC

wide

scanf functions

C, lc, or lC

To scan strings with scanf functions, and wscanf functions, use the above table with format type-specifiers s and S instead of c and C.

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