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scanf(3) Library Functions Manual scanf(3) NAME scanf, fscanf, sscanf - Converts formatted input LIBRARY Standard C Library (libc.so, libc.a) SYNOPSIS #include <stdio.h> int scanf( const char *format [,pointer]...); int fscanf( FILE *stream, const char *format [,pointer]...); int sscanf( const char *string, const char *format [,pointer]...); If the pointer parameter identifies an object of type wchar_t (see the DESCRIPTION section), source files should include either <sys/types.h> or <stddef.h> before <stdio.h> to maintain portability across all sys- tems that conform to current versions of ANSI, ISO, or X/Open stan- dards. STANDARDS Interfaces documented on this reference page conform to industry stan- dards as follows: fscanf(), scanf(), sscanf(): ISO C, XPG4, XPG4-UNIX Refer to the standards(5) reference page for more information about in- dustry standards and associated tags. PARAMETERS Specifies the format conversion. Specifies the input stream. Speci- fies input to be read. Points to the location to store the interpreted data. DESCRIPTION The scanf(), fscanf(), and sscanf() functions read character data, in- terpret it according to a format, and store the converted results into specified memory locations. The format parameter contains conversion specifications used to interpret the input. The pointer parameters specify where to store the interpreted data. These functions read their input from the following sources: Reads from standard input (stdin). Reads from the stream parameter. Reads from the character string specified by the string parameter. If the length of an input item is zero, these functions return an er- ror. This error indicates a matching failure unless end-of-file, an encoding error, or a read error prevented input from a stream, in which case the error indicates input failure. If there are insufficient arguments for format, the function's behavior is undefined. If format is exhausted while arguments remain, the ex- cess arguments are evaluated as always but are otherwise ignored. The format parameter can contain the following items: A conversion specification that directs the conversion of the next input field. Con- version specifications start with a % (percent sign). Any white-space character (as determined by the isspace() function) that matches 0 (zero) or more white-space characters in the input stream. Any charac- ter except % (percent sign) or a white-space character that must match the next character in the input stream. The input stream is broken into fields based on the following: White space All conversion specifications except %c, %C, and %[ ignore lead- ing white space and consider the first trailing white-space character as a field delimiter. Invalid character If the input stream contains a character that is not allowed, this invalid character delimits the field and is considered to be the first character of the next field. Maximum width If the conversion specification includes a maximum width and the field is not terminated by white space or an invalid character, the field is terminated when that character position is reached in the input stream. Conversion Specifications Each conversion specification in the format parameter has the following syntax: The character % (percent sign). The scanf() functions can handle a format string that enables the system to process elements of the pointer list in variable order. In such a case, the normal conversion character % (per- cent sign) is replaced by %digit$, where digit is a decimal num- ber in the range from 1 to NL_ARGMAX. Conversion is then applied to the specified pointer, rather than to the next unused pointer. This feature provides for the definition of format strings in an order appropriate to specific languages. If the variable ordering feature is used, it must be specified for all conversions except for conversion specifications that do not have corresponding pointers (conversion specifications with the * (asterisk) assignment suppression and %% conversion specifica- tions). If more than one conversion specification specifies the same digit, the results of the function are undefined. The op- tional assignment suppression character * (asterisk). An op- tional decimal digit string that specifies the maximum field width. An optional h or l indicating the size of the receiving variable for some conversion specifiers, as follows: An h fol- lowed by a d, i, o, u, or x conversion specifier indicates that the receiving variable will be treated as a short int or un- signed short int. An l followed by a d, i, o, u, or x conver- sion specifier indicates that the receiving variable will be treated as a long int or unsigned long int. An l followed by a e, f, or g indicates that the receiving variable will be treated as a double instead of a float. An l followed by a c, s, or [scanset] indicates that the receiving variable will be treated as wchar_t instead of char. A conversion code character that specifies the type of conversion to be applied: Accepts a single % (percent sign) input at this point; no assignment is done. Accepts an optionally signed decimal integer, whose format is the same as expected for the subject sequence of strtol() with the value 10 for the base argument. The pointer parameter should be an integer pointer. Accepts an optionally signed dec- imal integer, whose format is the same as expected for the sub- ject sequence of strtol() with the value 0 for the base argu- ment. The pointer parameter should be an integer pointer. Ac- cepts an unsigned decimal integer; the pointer parameter should be an unsigned integer pointer. Accepts an octal integer; the pointer parameter should be an integer pointer. Accepts a hexa- decimal integer; the pointer parameter should be an integer pointer. Accepts a floating-point number. The next field is converted accordingly and stored through the corresponding para- meter, which should be a pointer to a float. The input format for floating-point numbers is a string of digits, with the fol- lowing optional characteristics: It can be a signed value. It can be an exponential value, containing a decimal point followed by an exponent field, which consists of an E or an e followed by an optionally signed integer. It can be one of the special val- ues INF, NaNQ, or NaNS. This value is translated into the ANSI/IEEE value for infinity, quiet NaN, or signaling NaN, re- spectively. Matches an unsigned hexadecimal long integer, the same as the %p conversion of the printf() function. The corre- sponding argument will be a pointer to a pointer to void. No input is consumed. The corresponding argument is a pointer to an integer into which is written the number of characters read from the input stream by this function. The assignment count returned at the completion of this function is not incremented. Accepts a string of bytes that are not white-space characters. [ISO C] (When the current locale supports shift-state encoding, skipping white-space characters may result in redundant shift sequences.) If no l qualifier is present, the pointer parameter should point to an array of characters that is large enough to accept the converted sequence of characters, along with the terminating null byte automatically appended by the function. When inter- preting the input string, the function considers a white-space character as the delimiter of each input field and generates a string of char values as output. If a field width is given, the function assumes that pointer refers to a single-byte character array, and only the specified number of char values is read from the input string. [ISO C] If an l qualifier is present, the input is treated as a sequence of multibyte characters that begins in the initial shift state. The function converts each multibyte character to a wide-character as if by a call to the mbrtowc() function, with the conversion state described by an mbstate_t object initial- ized to zero before the first multibyte character is converted. The corresponding pointer should point to a wchar_t array that is large enough to accept the converted sequence of wide-charac- ters, plus the terminating null wide-character that is automati- cally added by the function. Accepts a string of multibyte characters and converts them as if by a call to the mbstowcs() function. The pointer parameter should be a pointer to an array of wchar_t. The array must be large enough to accept the string, along with the terminating null wide-character that is automati- cally added by the function. The function treats a white-space character as the delimiter of each field in the input string and generates a string of wchar_t as output. If the S conversion specifier includes a field width, the behavior of the conversion is undefined. Accepts a sequence of characters, the number of which is specified by the field width (1 if no field width is specified). If the l qualifier is not present, the corresponding argument should be a character array large enough to accept the converted sequence. The function does not append a terminating null char- acter to this sequence. [ISO C] If the l qualifier is present, the corresponding argu- ment is a sequence of multibyte characters that begins in the initial shift state. The function converts each multibyte char- acter as if by a call to the mbrtowc() function, with the con- version state described by an mbstate_t object initialized to zero before conversion of the first multibyte character. The corresponding argument should be a pointer to the first element of a wchar_t array that is large enough to accept the resulting sequence of wide-characters. The function does not append a ter- minating null wide-character to this sequence. The c directive suppresses the normal skip over white space; therefore, use %1s rather than %1c to read the next nonwhite- space character. Accepts a single character or a series of characters and converts to wchar_t type. If there is no field width or a field width of 1 in the conversion specification, one character is accepted and the pointer parameter should be a wchar_t pointer. If there is a field width greater than 1, the indicated number of characters are accepted and the pointer pa- rameter should be an array of wchar_t. The normal skip over white space is suppressed. Use %1S rather than %1C to read the next nonwhite-space character. Accepts as input the characters included in the scanset. The scanset parameter explicitly de- fines the characters that are accepted in the string data as those enclosed within [ ] (square brackets). If the l qualifier is not present, the corresponding pointer pa- rameter should point to an array of char that is large enough to contain the converted sequence and the terminating null charac- ter that is automatically added by the function. [ISO C] If the l qualifier is present, the input is handled as a sequence of multibyte characters that begins in the initial shift state. The function converts each multibyte character as if by a call to the mbrtowc() function, with the conversion state described by an mbstate_t object initialized to zero be- fore conversion of the first multibyte character. The corre- sponding pointer parameter should be a pointer to a wchar_t ar- ray large enough to accept the converted sequence and the termi- nating null wide-character that is automatically added by the function. The [scanset] directive suppresses the normal skip over leading white space. A scanset in the form of [^scanset] is an exclusive scanset; that is, the ^ (circumflex) serves as a complement operator and the characters in scanset are not accepted as input. Conventions used in the construction of the scanset are as fol- lows: You can represent a range of characters by the construct First-Last. Thus, you can express [0123456789] as [0-9]. The First parameter must be lexically less than or equal to Last; otherwise, the - (dash) stands for itself. The - also stands for itself whenever it is the first or the last character in the scanset. You can include the ] (right bracket) as an element of the scanset if it is the first character of the scanset. In this case, the right bracket is not interpreted as the bracket that closes the scanset. If the scanset is an exclusive scanset, the ] character is preceded by the ^ (circumflex) char- acter to make the ] an element of the scanset. The conversion specification syntax is summarized by the following syn- opsis: %[digit$][*][width][sizecode]convcode The results from the conversion are placed in *pointer unless you spec- ify assignment suppression with an * (asterisk). Assignment suppres- sion provides a way to describe an input field that is to be skipped. The input field is a string of nonwhite-space characters. It extends to the next inappropriate character or until the field width, if speci- fied, is exhausted. The conversion code indicates how to interpret the input field. The corresponding pointer must usually be of a restricted type. You should not specify the pointer parameter for a suppressed field. All *scanf() functions end at the end of the file, the end of the con- trol string, or when an input character conflicts with the control string. If the function ends with an input character conflict, the con- flicting character is not read from the input stream. Unless there is a match in the control string, these functions do not read trailing white space (including a newline character). The success of literal matches and suppressed assignments cannot be di- rectly determined. The *scanf() functions return only the number of successfully matched and assigned input items. RESTRICTIONS Currently, the DIGITAL UNIX product does not include locales that use shift-state encoding. Some sections of this reference page refer to the mb_state object or describe behavior that is dependent on shift- state encoding. This information is included only for your convenience in developing portable applications that run on multiple platforms, some of which may supply locales that do use shift-state encoding. RETURN VALUES The scanf(), fscanf(), and sscanf() functions return the number of suc- cessfully matched and assigned input items. This number can be 0 (zero) if there was an early conflict between an input character and the con- trol string. If the input ends before the first conflict or conversion, the functions return EOF (End-of-File). ERRORS The fscanf() function fails if either the stream is unbuffered, or the stream's buffer needs to be flushed and the function call causes an un- derlying read() or lseek() to be invoked and that operation fails. In addition, the scanf(), fscanf(), and sscanf() functions set errno to the corresponding value for the following conditions: [Digital] The O_NONBLOCK flag is set for the underlying stream and the process would be delayed by the read operation. [Digital] The file descriptor un- derlying the stream is not a valid file descriptor or is not open for reading. The input byte sequence does not form a valid character. [Digital] The read operation was interrupted by a signal that was caught and no data was transferred. [Digital] The call is attempting to read from the process's controlling terminal and either the process group is orphaned or the process is ignoring or blocking the SIGTTIN signal. [Digital] Insufficient memory is available for the operation. RELATED INFORMATION Functions: atof(3), atoi(3), getc(3), getwc(3), mbstowcs(3), mbtowc(3), printf(3), wprintf(3), wscanf(3) Standards: standards(5) delim off scanf(3)