scanf(3S) scanf(3S)NAME scanf, fscanf, sscanf - convert formatted input SYNOPSIS #include <stdio.h> int scanf(format [, pointer]... ) char *format; int fscanf(stream, format [, pointer]... ) FILE *stream; char *format; int sscanf(s, format [, pointer]... ) char *s, *format; DESCRIPTION scanf reads from the standard input stream stdin. fscanf reads from the named input stream. sscanf reads from the character string at *s. Each function reads characters, in- terprets them according to format, and stores the results in the location specified by the pointer arguments. Each func- tion expects as arguments: a control string format (described below) and a set of pointer arguments indicating where the converted input should be stored. The control string usually contains conversion specifica- tions, which are used to direct interpretation of input se- quences. The control string may contain: 1. White-space characters (blanks and tabs) which, except in two cases described below, cause input to be read up to the next nonwhite-space character. 2. An ordinary character (not %), which must match the next character of the input stream. 3. Conversion specifications, consisting of the character %, an optional assignment suppression character *, an op- tional numerical maximum field width, an optional letter l or h indicating the size of the receiving variable, and a conversion code. A conversion specification directs the conversion of the next input field; the result is placed in the variable pointed to by the corresponding argument, unless assignment suppression has been indicated by *. The suppression of as- signment provides a way of describing an input field which is to be skipped. An input field is defined as a string of nonwhite-space characters; it extends to the next inap- propriate character or until the field width, if specified, is exhausted. For all descriptors except ``['' and ``c'', white space leading an input field is ignored. April, 1990 1
scanf(3S) scanf(3S)The conversion code indicates the interpretation of the in- put field; the corresponding pointer argument must usually be of a restricted type. For a suppressed field, no pointer argument should be given. The following conversion codes are legal: % A single % is expected in the input at this point; no assignment is done. d A decimal integer is expected; the corresponding ar- gument should be an integer pointer. u An unsigned decimal integer is expected; the corresponding argument should be an unsigned integer pointer. o An octal integer is expected; the corresponding argu- ment should be an integer pointer. x A hexadecimal integer is expected; the corresponding argument should be an integer pointer. e,f,g A floating point number is expected; the next field is converted accordingly and stored through the corresponding argument, which should be a pointer to a float. The input format for floating point numbers is an optionally signed string of digits, possibly containing a decimal point, followed by an optional exponent field consisting of an E or an e, followed by an optional +, -, or space followed by an integer. s A character string is expected; the corresponding ar- gument should be a character pointer to an array of characters large enough to accept the string and a terminating \0, which will be added automatically. The input field is terminated by a white-space char- acter. c A character is expected; the corresponding argument should be a character pointer. The normal skip over white space is suppressed in this case; to read the next nonspace character, use %1s. If a field width is given, the corresponding argument should refer to a character array; the indicated number of characters is read. [ String data and the normal skip over leading white space is suppressed. The left bracket is followed by a set of characters (the scanset) and a right brack- et; the input field is the maximal sequence of input characters consisting entirely of characters in the scanset. The caret, (^), when it appears as the 2 April, 1990
scanf(3S) scanf(3S)first character in the scanset, serves as a comple- ment operator and redefines the scanset as the set of all characters not contained in the remainder of the scanset string. There are some conventions used in the construction of the scanset. A range of charac- ters may be represented by the construct first-last; thus, [0123456789] may be expressed [0-9]. Using this convention, first must be lexically less than or equal to last, or else the dash will stand for it- self. The dash will also stand for itself whenever it is the first or the last character in the scanset. To include the right square bracket as an element of the scanset, it must appear as the first character (possibly preceded by a circumflex) of the scanset; otherwise it will be interpreted syntactically as the closing bracket. The corresponding argument must point to a character array large enough to hold the data field and the terminating \0, which will be ad- ded automatically. At least one character must match for this conversion to be considered successful. The conversion characters d, u, o, and x may be preceded by l or h to indicate that a pointer to long or short, rather than int, is in the argument list. Similarly, the conver- sion characters e, f, and g may be preceded by l to indicate that a pointer to double, rather than float, is in the argu- ment list. The l or h modifier is ignored for other conversion charac- ters. scanf conversion terminates at EOF, at the end of the control string, or when an input character conflicts with the control string. In the latter case, the offending char- acter is left unread in the input stream. scanf returns the number of successfully matched and as- signed input items; this number can be zero when an early conflict between an input character and the control string occurs. If the input ends before the first conflict or conversion, EOF is returned. EXAMPLES The call: int i; n; float x; char name[50]; n = scanf ("%d%f%s", &i, &x, name); with the input line 25 54.32E-1 thompson will assign the value 3 to n, the value 25 to i, and the value 5.432 to x; name will contain thompson\0. April, 1990 3
scanf(3S) scanf(3S)The call int i; float x; char name[50]; (void) scanf ("%2d%f%*d %[0-9]", &i, &x, name); with input 56789 0123 56a72 will assign 56 to i, 789.0 to x, skip 0123, and place the string 56\0 in name. The next call to getchar (see getc(3S)) will return a. RETURN VALUE These functions return EOF on end of input and a short count for missing or illegal data items. NOTES Trailing white space is left unread unless matched in the control string. BUGS The success of literal matches and suppressed assignments is not directly determinable. SEE ALSO getc(3S), printf(3S), strtod(3C), strtol(3C). 4 April, 1990