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C166 User's Guide

C166 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming Error Messages Library Reference Library Files Source Code Standard Types jmp_buf ptrdiff_t size_t va_list wchar_t Macros HARRAY HVAR MARRAY MVAR XARRAY XVAR Routines By Category Buffer Manipulation Routines Character Routines Data Conversion Routines Intrinsic Routines Math Routines Memory Allocation Routines Stream I/O Routines String Routines Variable Length Argument Routines Miscellaneous Routines Include Files SFR Definitions absacc.h assert.h ctype.h float.h intrins.h limits.h math.h membox.h setjmp.h stdarg.h stddef.h stdio.h stdlib.h string.h Reference _alloc_boxf _alloc_boxh _alloc_boxn _atomic_ _bfld_ _calloc_boxf _calloc_boxh _calloc_boxn _chkdouble_ _chkfloat_ _crol_ _cror_ _diswdt_ _einit_ _endatomic_ _free_boxf _free_boxh _free_boxn _getkey _idle_ _init_boxf _init_boxh _init_boxn _irol_ _iror_ _lrol_ _lror_ _nop_ _pop_ _prior_ _priord_ _push_ _pwrdn_ _sof_ _srvwdt_ _testclear_ _testset_ _tolower _toupper _trap_ abs acos asin assert atan atan2 atof atoi atol calloc calloc_b ceil cos cosh exp fabs floor fmemccpy fmemchr fmemcmp fmemcpy fmemmove fmemset fmod free free_b fstrcat fstrchr fstrcmp fstrcpy fstrcspn fstrlen fstrncat fstrncmp fstrncpy fstrpbrk fstrpos fstrrchr fstrrpbrk fstrrpos fstrspn getchar gets hmemcmp hmemcpy hstrcmp hstrcpy init_mempool init_mempool_b isalnum isalpha iscntrl isdigit isgraph islower isprint ispunct isspace isupper isxdigit labs log log10 longjmp malloc malloc_b memccpy memchr memcmp memcpy memmove memset modf offsetof pow printf putchar puts rand realloc realloc_b scanf setjmp sin sinh sprintf sqrt srand sscanf strcat strchr strcmp strcpy strcspn strlen strncat strncmp strncpy strpbrk strpos strrchr strrpbrk strrpos strspn strstr strtod strtol strtoul tan tanh toascii toint tolower toupper ungetchar va_arg va_end va_start vprintf vsprintf xcalloc xfree xinit_mempool xmalloc xmemccpy xmemchr xmemcmp xmemcpy xmemmove xmemset xrealloc xstrcmp xstrcpy xstrlen xstrncpy Appendix


#include <stdio.h>

int scanf (
  const char *fmtstr       /* format string */
  <[>, arguments ...<]>);    /* additional arguments */

The scanf function reads data from the input stream using the getchar routine. Data input are stored in the locations specified by argument according to the format string fmtstr. Each argument must be a pointer to a variable that corresponds to the type defined in fmtstr. The type controls the interpretation of the input data. The fmtstr may be composed of one or more whitespace characters, non-whitespace characters, and format specifications.

  • Whitespace characters, blank (' '), tab ('\t'), or newline ('\n'), cause scanf to skip whitespace characters in the input stream. A single whitespace character in the format string matches 0 or more whitespace characters in the input stream.
  • Non-whitespace characters, with the exception of the percent sign ('%'), cause scanf to read but not store a matching character from the input stream. The scanf function terminates if the next character in the input stream does not match the specified non-whitespace character.
  • Format specifications begin with a percent sign ('%') and cause scanf to read and convert characters from the input stream to the specified type values. The converted value is stored to an argument from the parameter list. Characters following a percent sign that are not recognized as a format specification are treated as ordinary characters. For example, %% matches a single percent sign in the input stream.

The format string is read from left to right. Characters that are not part of the format specifications must match characters in the input stream. These characters are read from the input stream but are discarded and not stored. If a character in the input stream conflicts with the format string, scanf terminates. Any conflicting characters remain in the input stream.

The first format specification encountered in the format string references the first argument after fmtstr. The scanf function converts input characters and stores the value using the format specification. The second format specification accesses the second argument after fmtstr, and so on. If there are more arguments than format specifications, the extra arguments are ignored. Results are unpredictable if there are not enough arguments for the format specifications.

Values in the input stream are called input fields and are delimited by whitespace characters. When converting input fields, scanf ends a conversion for an argument when a whitespace character or another unrecognized character is encountered.

Format specifications have the following format:

% <[>*<]> <[>width<]> <[>{b|h|l}<]> type

Each field in the format specification can be a single character or a number which specifies a particular format option.

The type field is where a single character specifies whether input characters are interpreted as a character, string, or number. This field can be any one of the characters in the following table.

Character Argument Type Input Format
d int * Signed decimal number.
i int * Signed decimal, hexadecimal, or octal integer.
u unsigned int * Unsigned decimal number.
o unsigned int * Unsigned octal number.
x unsigned int * Unsigned hexadecimal number.
e float * Floating-point number.
f float * Floating-point number.
g float * Floating-point number.
c char * A single character.
s char * A string of characters terminated by whitespace.

An asterisk ('*') as the first character of a format specification causes the input field to be scanned but not stored. The asterisk suppresses assignment of the format specification.

The width field is a non-negative number that specifies the maximum number of characters read from the input stream. No more than width characters are read and converted for the corresponding argument. However, fewer than width characters may be read if a whitespace or other unrecognized character is encountered first.

The optional characters b, h, and l may immediately precede the type character to respectively specify char, short, or long versions of the integer types d, i, u, o, and x. If l is applied to the floating-point types f, e, and g, a pointer to a double is required as an argument.


  • This function is implementation-specific and is based on the operation of the _getkey and putchar functions. These functions, as provided in the standard library, read and write characters using the microcontroller's serial port. Custom functions may use other I/O devices.
Return Value

The scanf function returns the number of input fields that were successfully converted. An EOF is returned if an error is encountered.

See Also

gets, printf, putchar, puts, sprintf, vprintf, vsprintf

#include <stdio.h>

void tst_scanf (void) {
  char a;
  int b;
  long c;

  unsigned char x;
  unsigned int y;
  unsigned long z;

  float f,g;
  char d, buf [10];
  int argsread;

  printf ("Enter a signed byte, int, and long\n");
  argsread = scanf ("%bd %d %ld", &a, &b, &c);
  printf ("%d arguments read\n", argsread);

  printf ("Enter an unsigned byte, int, and long\n");
  argsread = scanf ("%bu %u %lu", &x, &y, &z);
  printf ("%d arguments read\n", argsread);

  printf ("Enter a character and a string\n");
  argsread = scanf ("%c %9s", &d, buf);
  printf ("%d arguments read\n", argsread);

  printf ("Enter two floating-point numbers\n");
  argsread = scanf ("%f %f", &f, &g);
  printf ("%d arguments read\n", argsread);
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