scanf(S) 6 January 1993 scanf(S) Name scanf - convert formatted input Syntax cc . . . -lc #include <stdio.h> int scanf (format [, pointer ] . . . const char *format; int fscanf (stream, format [, pointer ] . . . FILE *stream; const char *format; int sscanf (s, format [, pointer ] . . . char *s; const char *format; Description The scanf function reads from the standard input stream stdin. fscanf reads from the named input stream. sscanf reads from the character string s. Each function reads characters, interprets them according to a format, and stores the results in its arguments. Each expects, as argu- ments, a control string format described below, and a set of pointer arguments indicating where the converted input should be stored. The results are undefined in that there are insufficient args for the format. If the format is exhausted while args remain, the excess args are simply ignored. The control string usually contains conversion specifications, which are used to direct interpretation of input sequences. The control string may contain: 1. White-space characters (blanks, tabs, new-lines, or form-feeds) which, except in two cases described below, cause input to be read up to the next non-white-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 suppressing character *, an optional numerical maximum field width, an optional l (ell) 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 corre- sponding argument, unless assignment suppression was indicated by *. The suppression of assignment provides a way of describing an input field which is to be skipped. An input field is defined as a string of non- space characters; it extends to the next inappropriate character or until the field width, if specified, is exhausted. For all descriptors except ``['' and ``c'', white space leading an input field is ignored. The conversion code indicates the interpretation of the input field; the corresponding pointer argument must usually be of a restricted type. For a suppressed field, no pointer argument is given. The following conver- sion 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 argument 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 argument should be an integer pointer. x a hexadecimal integer is expected; the corresponding argument should be an integer pointer. i an integer is expected; the corresponding argument should be an integer pointer. It stores the value of the next input item inter- preted according to C conventions: a leading ``0'' implies octal; a leading ``0x'' implies hexadecimal; otherwise, decimal. n stores in an integer argument the total number of characters (including white space) that have been scanned so far since the function call. No input is consumed. 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 - , fol- lowed by an integer. s a character string is expected; the corresponding argument should be a character pointer pointing to an array of characters large enough to accept the string and a terminating \0, which is added automatically. The input field is terminated by a white-space character. 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 non-space 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. [ indicates string data and the normal skip over leading white space is suppressed. The left bracket is followed by a set of charac- ters, which is called the scanset, and a right bracket; the input field is the maximal sequence of input characters consisting entirely of characters in the scanset. The caret (^), when it appears as the first character in the scanset, serves as a comple- ment operator and redefines the scanset as the set of all charac- ters not contained in the remainder of the scanset string. There are some conventions used in the construction of the scanset. A range of characters 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 stands for itself. The dash also stands 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 caret) of the scanset, and in this case it is not syntactically interpreted as the closing bracket. The corresponding argument must point to a character array large enough to hold the data field and the ter- minating \0, which is added automatically. At least one character must match for this conversion to be considered successful. The conversion characters d, u, o, x and i may be preceded by l or h to indicate that a pointer to long or to short rather than to int is in the argument list. Similarly, the conversion characters e, f, and g may be preceded by l to indicate that a pointer to double rather than to float is in the argument list. The l or h modifier is ignored for other conversion characters. The scanf function conversion terminates at EOF, at the end of the con- trol string, or when an input character conflicts with the control string. In the latter case, the offending character is left unread in the input stream. The scanf function returns the number of successfully matched and assigned input items; this number can be zero in the event of an early conflict between an input character and the control string. If the input ends before the first conflict or conversion, EOF is returned. Diagnostics These functions return EOF on end of input and an int count for missing or illegal data items. Notes Trailing white space (including a new-line) is left unread unless matched in the control string. scanf has a file limit of FOPENMAX; for more information see stdio(S). See also getc(S), printf(S), stdio(S), strtod(S), strtol(S) Standards conformance fscanf, scanf and sscanf are conformant with: AT&T SVID Issue 2; X/Open Portability Guide, Issue 3, 1989; ANSI X3.159-1989 Programming Language -- C; IEEE POSIX Std 1003.1-1990 System Application Program Interface (API) [C Language] (ISO/IEC 9945-1); and NIST FIPS 151-1. Examples The call: int n ; float x; char name[50]; n = scanf("%d%f%s", &i, &x, name); with the input line: 25 54.32E-1 thompson assigns to n the value 3, to i the value 25, to x the value 5.432, and name contains thompson\0 . Or: int i, j; float x; char name[50]; (void) scanf("%i%2d%f%*d %[0-9] ", &j, &i, &x, name); with input: 011 56789 0123 56a72 assigns 9 to j, 56 to i, 789.0 to x, skip 0123, and place the string 56\0 in name. The next call to getchar (see getc(S)) returns a. Or: int i, j, s, e; char name[50]; (void) scanf("%i %i %n%s%n", &i, &j, &s, name, &e); with input: 0x11 0xy johnson assigns 17 to i, 0 to j, 6 to s, places the string xy\0 in name, and assigns 8 to e. Thus, the length of name is e - s = 2 . The next call to getchar (see getc(S)) returns a blank.