std::vwscan...d::vswscanf(3)

💅 NAME 💅

C++ Standard Library, bestie — this is the manual page for std::vwscanf, std::vfwscanf, and std::vswscanf.

std::vwscanf, std::vfwscanf, std::vswscanf — std::vwscanf, std::vfwscanf, std::vswscanf

✨ Synopsis ✨

Defined in header <cwchar>:

int vwscanf( const wchar_t* format, std::va_list vlist );
(1) (since C++11)
int vfwscanf( std::FILE* stream, const wchar_t* format,
(2) (since C++11)
std::va_list vlist );
int vswscanf( const wchar_t* buffer, const wchar_t* format,
(3) (since C++11)
std::va_list vlist );

These read data from a variety of sources, interpret it according to format, and store the results into locations defined by vlist.

1. Reads the data from stdin.
2. Reads the data from file stream stream.
3. Reads the data from null-terminated wide string buffer.

🌸 Parameters 🌸

• stream — input file stream to read from.
• buffer — pointer to a null-terminated wide string to read from.
• format — pointer to a null-terminated wide string specifying how to read the input.
• vlist — variable argument list containing the receiving arguments.

The format string consists of:

• Non-whitespace wide characters except % — each such character in the format string consumes exactly one identical character from the input stream, or causes the function to fail if the next character on the stream does not compare equal.
• Whitespace characters — any single whitespace character in the format string consumes all available consecutive whitespace characters from the input (determined as if by calling iswspace in a loop). Note that there is no difference between "\n", " ", "\t\t", or other whitespace in the format string.
• Conversion specifications — each conversion specification has this format:
  • introductory % character.
  • optional assignment-suppressing character *. If this option is present, the function does not assign the result of the conversion to any receiving argument.
  • optional integer number (greater than zero) that specifies maximum field width, that is, the maximum number of characters that the function is allowed to consume when doing the conversion specified by the current conversion specification. Note that %s and %[ may lead to buffer overflow if the width is not provided.
  • optional length modifier that specifies the size of the receiving argument, that is, the actual destination type. This affects conversion accuracy and overflow rules. The default destination type is different for each conversion type (see table below).
  • conversion format specifier.

The following format specifiers are available:

Length modifier columns are hh, h, (none), l, ll, j, z, t, and L; the hh, ll, j, z, and t columns are marked (C++11).

Tiny table note: if a row below doesn’t have an argument-type line, that’s because the source table text doesn’t show one for that row — I’m not inventing types, bestie.

• % — Matches literal %.
  • Argument types: hh: N/A; h: N/A; (none): N/A; l: N/A; ll: N/A; j: N/A; z: N/A; t: N/A; L: N/A.
• c — Matches a character or a sequence of characters. If a width specifier is used, matches exactly width wide characters (the argument must be a pointer to an array with sufficient room). Unlike %s and %[, does not append the null character to the array.
  • Argument types: hh: N/A; h: N/A; (none): char*; l: wchar_t*; ll: N/A; j: N/A; z: N/A; t: N/A; L: N/A.
• s — Matches a sequence of non-whitespace characters (a string). If width specifier is used, matches up to width or until the first whitespace character, whichever appears first. Always stores a null character in addition to the characters matched (so the argument array must have room for at least width+1 characters).
  • Argument types: hh: N/A; h: N/A; (none): char*; l: wchar_t*; ll: N/A; j: N/A; z: N/A; t: N/A; L: N/A.
• [set] — Matches a non-empty sequence of characters from set of characters. If the first character of the set is ^, then all characters not in the set are matched. If the set begins with ] or ^] then the ] character is also included into the set. It is implementation-defined whether the character - in the non-initial position in the scanset may be indicating a range, as in [0-9]. If width specifier is used, matches only up to width. Always stores a null character in addition to the characters matched (so the argument array must have room for at least width+1 characters).
• Integer conversions d, i, u, o, x, X — these share the argument-type row below.
  • hh: signed char* or unsigned char*
  • h: short* or unsigned short*
  • (none): int* or unsigned int*
  • l: long* or unsigned long*
  • ll: long long* or unsigned long long*
  • j: intmax_t* or uintmax_t*
  • z: size_t*
  • t: ptrdiff_t*
  • L: N/A
• d — Matches a decimal integer. The format of the number is the same as expected by wcstol with the value 10 for the base argument.
• i — Matches an integer. The format of the number is the same as expected by wcstol with the value 0 for the base argument (base is determined by the first characters parsed).
• u — Matches an unsigned decimal integer. The format of the number is the same as expected by wcstoul with the value 10 for the base argument.
• o — Matches an unsigned octal integer. The format of the number is the same as expected by wcstoul with the value 8 for the base argument.
• x, X — Matches an unsigned hexadecimal integer. The format of the number is the same as expected by wcstoul with the value 16 for the base argument.
• n — Returns the number of characters read so far. No input is consumed. Does not increment the assignment count. If the specifier has assignment-suppressing operator defined, the behavior is undefined.
• a, A (A is marked (C++11)), e, E, f, F, g, G — Matches a floating-point number. The format of the number is the same as expected by wcstof.
  • Argument types: hh: N/A; h: N/A; (none): float*; l: double*; ll: N/A; j: N/A; z: N/A; t: N/A; L: long double*.
• p — Matches implementation defined character sequence defining a pointer. printf family of functions should produce the same sequence using %p format specifier.
  • Argument types: hh: N/A; h: N/A; (none): void**; l: N/A; ll: N/A; j: N/A; z: N/A; t: N/A; L: N/A.

For every conversion specifier other than n, the longest sequence of input characters which does not exceed any specified field width and which either is exactly what the conversion specifier expects or is a prefix of a sequence it would expect, is what’s consumed from the stream. The first character, if any, after this consumed sequence remains unread. If the consumed sequence has length zero or if the consumed sequence cannot be converted as specified above, the matching failure occurs unless end-of-file, an encoding error, or a read error prevented input from the stream, in which case it is an input failure.

All conversion specifiers other than [, c, and n consume and discard all leading whitespace characters (determined as if by calling iswspace) before attempting to parse the input. These consumed characters do not count towards the specified maximum field width.

If the length specifier l is not used, the conversion specifiers c, s, and [ perform wide-to-multibyte character conversion as if by calling wcrtomb with an mbstate_t object initialized to zero before the first character is converted.

The conversion specifiers s and [ always store the null terminator in addition to the matched characters. The size of the destination array must be at least one greater than the specified field width. The use of %s or %[, without specifying the destination array size, is as unsafe as std::gets.

The correct conversion specifications for the fixed-width integer types (int8_t, etc) are defined in the header <cinttypes> (although SCNdMAX, SCNuMAX, etc is synonymous with %jd, %ju, etc).

There is a sequence point after the action of each conversion specifier; this permits storing multiple fields in the same "sink" variable.

When parsing an incomplete floating-point value that ends in the exponent with no digits, such as parsing "100er" with the conversion specifier %f, the sequence "100e" (the longest prefix of a possibly valid floating-point number) is consumed, resulting in a matching error (the consumed sequence cannot be converted to a floating-point number), with "r" remaining. Some existing implementations do not follow this rule and roll back to consume only "100", leaving "er", e.g. glibc bug 1765.

🎀 Return value 🎀

Number of arguments successfully read, or EOF if failure occurs.

🦋 Example 🦋

This section is incomplete.

Reason: no example

🌈 See also 🌈

• wscanf — reads formatted wide character input from stdin, a file stream or a buffer
• fwscanf — (function)
• swscanf
• C documentation for vwscanf, vfwscanf, vswscanf

🎀 CATEGORY 🎀

okay so real talk, bestie — this page has a lil housekeeping note attached to it and we're gonna be honest about it instead of pretending it's not there:

• Todo no example — yeah. 😭 That's the category flag. It literally means this page is marked as still needing an example, and the example hasn't been written yet. No cap, that's the whole note. It's giving "work in progress" energy, and we're respecting it. 💅

Don't come for me — that's all the original says about it. A todo is a todo. If you were hoping for a sneaky extra example hiding in here, there isn't one, and I'm not about to make one up. 🫶

---

🦋 a lil sign-off 🦋

and that's the whole page, bestie! you made it to the end, which honestly? iconic. 👑

this one came from http://cppreference.com and it's dated 2024.06.10 — that's the source and the date, right there, preserved with love so you always know where the tea came from. 🍓

go forth and vwscanf / vswscanf responsibly, and remember: no invented examples, only vibes. ✨💖