Scan Conversion Specifiers

Following any field width, you must write a one-character scan conversion specifier, either a one-character code or a scan set, possibly preceded by a one-character qualifier. Each combination determines the type required of the next argument (if any) and how the scan functions interpret the text sequence and converts it to an encoded value. The integer and floating-point conversions also determine what base to assume for the text representation. (The base is the base argument to the functions strtol and strtoul.) The following table lists all defined combinations and their properties.

Conversion  Argument          Conversion
 Specifier    Type             Function  Base
   %c       char x[]
  %lc       wchar_t x[]
   %d       int *x             strtol     10
  %hd       short *x           strtol     10
  %ld       long *x            strtol     10
   %e       float *x           strtod     10
  %le       double *x          strtod     10
  %Le       long double *x     strtod     10
   %E       float *x           strtod     10
  %lE       double *x          strtod     10
  %LE       long double *x     strtod     10
   %f       float *x           strtod     10
  %lf       double *x          strtod     10
  %Lf       long double *x     strtod     10
   %g       float *x           strtod     10
  %lg       double *x          strtod     10
  %Lg       long double *x     strtod     10
   %G       float *x           strtod     10
  %lG       double *x          strtod     10
  %LG       long double *x     strtod     10
   %i       int *x             strtol      0
  %hi       short *x           strtol      0
  %li       long *x            strtol      0
   %n       int *x
  %hn       short *x
  %ln       long *x
   %o       unsigned int *x    strtoul     8
  %ho       unsigned short *x  strtoul     8
  %lo       unsigned long *x   strtoul     8
   %p       void **x
   %s       char x[]
  %ls       wchar_t x[]
   %u       unsigned int *x    strtoul    10
  %hu       unsigned short *x  strtoul    10
  %lu       unsigned long *x   strtoul    10
   %x       unsigned int *x    strtoul    16
  %hx       unsigned short *x  strtoul    16
  %lx       unsigned long *x   strtoul    16
   %X       unsigned int *x    strtoul    16
  %hX       unsigned short *x  strtoul    16
  %lX       unsigned long *x   strtoul    16
 %[...]     char x[]
%l[...]     wchar_t x[]
   %%       none

The scan conversion specifier (or scan set ) determines any behavior not summarized in this table. In the following descriptions, examples follow each of the scan conversion specifiers. In each example, the function sscanf matches the bold characters.

You write %c to store the matched input characters in an array object. If you specify no field width w, then w has the value one. The match does not skip leading white space. Any sequence of w characters matches the conversion pattern.

sscanf(“129E-2”, “%c”, &c)             stores '1'
sscanf(“129E-2”, “%2c”, &c[0])         stores '1', '2'

For a wide stream, conversion occurs as if by repeatedly calling wcrtomb, beginning in the initial conversion state.

swscanf(L“129E-2”, L“%c”, &c)          stores '1'

You write %lc to store the matched input characters in an array object, with elements of type wchar_t. If you specify no field width w, then w has the value one. The match does not skip leading white space. Any sequence of w characters matches the conversion pattern. For a byte stream, conversion occurs as if by repeatedly calling mbrtowc, beginning in the initial conversion state.

sscanf(“129E-2”, “%lc”, &c)            stores L'1'
sscanf(“129E-2”, “%2lc”, &c)           stores L'1', L'2'
swscanf(L“129E-2”, L“%lc”, &c)         stores L'1'

You write %d, %i, %o, %u, %x, or %X to convert the matched input characters as a signed integer and store the result in an integer object.

sscanf(“129E-2”, “%o%d%x”, &i, &j, &k) stores 10, 9, 14

You write %e, %E, %f, %g, or %G to convert the matched input characters as a signed fraction, with an optional exponent, and store the result in a floating-point object.

sscanf(“129E-2”, “%e”, &f)             stores 1.29

You write %n to store the number of characters matched (up to this point in the format) in an integer object. The match does not skip leading white space and does not match any input characters.

sscanf(“129E-2”, “12%n”, &i)           stores 2

You write %p to convert the matched input characters as an external representation of a pointer to void and store the result in an object of type pointer to void. The input characters must match the form generated by the %p print conversion specification.

sscanf(“129E-2”, “%p”, &p)             stores, e.g. 0x129E

You write %s to store the matched input characters in an array object, followed by a terminating null character. If you do not specify a field width w, then w has a large value. Any sequence of up to w non white-space characters matches the conversion pattern.

sscanf(“129E-2”, “%s”, &s[0])          stores “129E-2”

For a wide stream, conversion occurs as if by repeatedly calling wcrtomb beginning in the initial conversion state.

swscanf(L“129E-2”, L“%s”, &s[0])       stores “129E-2”

You write %ls to store the matched input characters in an array object, with elements of type wchar_t, followed by a terminating null wide character. If you do not specify a field width w, then w has a large value. Any sequence of up to w non white-space characters matches the conversion pattern. For a byte stream, conversion occurs as if by repeatedly calling mbrtowc, beginning in the initial conversion state.

sscanf(“129E-2”, “%ls”, &s[0])         stores L“129E-2”
swscanf(L“129E-2”, L“%ls”, &s[0])      stores L“129E-2”

You write %[ to store the matched input characters in an array object, followed by a terminating null character. If you do not specify a field width w, then w has a large value. The match does not skip leading white space. A sequence of up to w characters matches the conversion pattern in the scan set that follows. To complete the scan set, you follow the left bracket ([) in the conversion specification with a sequence of zero or more match characters, terminated by a right bracket (]).

If you do not write a caret (^) immediately after the [, then each input character must match one of the match characters. Otherwise, each input character must not match any of the match characters, which begin with the character following the ^. If you write a ] immediately after the [ or [^, then the ] is the first match character, not the terminating ]. If you write a minus (-) as other than the first or last match character, an implementation can give it special meaning. It usually indicates a range of characters, in conjunction with the characters immediately preceding or following, as in 0-9 for all the digits.) You cannot specify a null match character.

sscanf(“129E-2”, “[54321]”, &s[0])     stores “12”

For a wide stream, conversion occurs as if by repeatedly calling wcrtomb, beginning in the initial conversion state.

swscanf(L“129E-2”, L“[54321]”, &s[0])  stores “12”

You write %l[ to store the matched input characters in an array object, with elements of type wchar_t, followed by a terminating null wide character. If you do not specify a field width w, then w has a large value. The match does not skip leading white space. A sequence of up to w characters matches the conversion pattern in the scan set that follows.

For a byte stream, conversion occurs as if by repeatedly calling mbrtowc, beginning in the initial conversion state.

sscanf(“129E-2”, “l[54321]”, &s[0])    stores L“12”
swscanf(L“129E-2”, L“l[54321]”, &s[0]) stores L“12”

You write %% to match the percent character (%). The function does not store a value.

sscanf(“%  0XA”, “%% %i”)              stores 10