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Cx51 Introduction Compiling Programs Language Extensions Preprocessor Advanced Programming 8051 Derivatives Error Messages Library Reference Library Files Source Code Standard Types jmp_buf size_t va_list wchar_t Macros CBYTE CWORD DBYTE DWORD FARRAY FCARRAY FCVAR FVAR PBYTE PWORD XBYTE XWORD 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 80c517.h absacc.h assert.h ctype.h float.h intrins.h limits.h math.h rtx51tny.h setjmp.h stdarg.h stddef.h stdio.h stdlib.h string.h Reference _chkfloat_ _crol_ _cror_ _getkey _irol_ _iror_ _lrol_ _lror_ _nop_ _pop_ _push_ _testbit_ _tolower _toupper abs acos acos517 asin asin517 assert atan atan2 atan517 atof atof517 atoi atol cabs calloc ceil cos cos517 cosh exp exp517 fabs floor fmod free getchar gets init_mempool isalnum isalpha iscntrl isdigit isgraph islower isprint ispunct isspace isupper isxdigit labs log log10 log10517 log517 longjmp malloc memccpy memchr memcmp memcpy memmove memset modf offsetof pow printf printf517 putchar puts rand realloc scanf scanf517 setjmp sin sin517 sinh sprintf sprintf517 sqrt sqrt517 srand sscanf sscanf517 strcat strchr strcmp strcpy strcspn strlen strncat strncmp strncpy strpbrk strpos strrchr strrpbrk strrpos strspn strstr strtod strtod517 strtok strtol strtoul switchbank tan tan517 tanh toascii toint tolower toupper ungetchar va_arg va_end va_start vprintf vsprintf Appendix

scanf

Summary
#include <stdio.h>

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

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.

Note

  • 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.
  • The total number of bytes that may be passed to this function is limited due to the memory restrictions imposed by the 8051. A maximum of 15 bytes may be passed in SMALL or COMPACT model. A maximum of 40 bytes may be passed in LARGE model.
  • Problems may occur in some instances when the _getkey function requires overlayable data memory. Refer to the Keil Knowledgebase Article for more information.
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, printf517, putchar, puts, scanf517, sprintf517, sscanf, sscanf517, vprintf, vsprintf

Example
#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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