wscanf, fwscanf, swscanf, wscanf_s, fwscanf_s, swscanf_s

int wscanf( const wchar_t *format, ... );

int wscanf( const wchar_t *restrict format, ... );

int fwscanf( FILE *stream, const wchar_t *format, ... );

int fwscanf( FILE *restrict stream,
             const wchar_t *restrict format, ... );

int swscanf( const wchar_t *buffer, const wchar_t *format, ... );

int swscanf( const wchar_t *restrict buffer,
             const wchar_t *restrict format, ... );

int wscanf_s( const wchar_t *restrict format, ...);

int fwscanf_s( FILE *restrict stream,
               const wchar_t *restrict format, ...);

int swscanf_s( const wchar_t *restrict s,
               const wchar_t *restrict format, ...);

Reads data from the a variety of sources, interprets it according to format and stores the results into given locations.

Parameters

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 the following 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 the 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:

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 gets.

The correct conversion specifications for the fixed-width integer types (int8_t, etc) are defined in the header <inttypes.h> (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

Example

#include <stdio.h>
#include <wchar.h>
#include <string.h>
 
#define NUM_VARS   3
#define ERR_READ   2
#define ERR_WRITE  3
 
int main(void) {
    wchar_t state[64];
    wchar_t capital[64];
    unsigned int population = 0;
    int elevation = 0;
    int age = 0;
    float pi = 0;
 
#if INTERACTIVE_MODE
    wprintf(L"Enter state, age, and pi value: ");
    if (wscanf(L"%ls%d%f", state, &age, &pi) != NUM_VARS) {
        fprintf(stderr, "Error reading input.\n");
        return ERR_READ;
    }
#else
    wchar_t* input = L"California 170 3.141592";
    if (swscanf(input, L"%ls%d%f", state, &age, &pi) != NUM_VARS) {
        fprintf(stderr, "Error reading input.\n");
        return ERR_READ;
    }
#endif
    wprintf(L"State: %ls\nAge  : %d years\nPi   : %.5f\n\n", state, age, pi);
 
    FILE* fp = tmpfile();
    if (fp) {
        // write some data to temp file
        if (!fwprintf(fp, L"Mississippi Jackson 420000 807")) {
            fprintf(stderr, "Error writing to file.\n");
            fclose(fp);
            return ERR_WRITE;
        }
        // rewind file pointer
        rewind(fp);
 
        // read data into variables
        fwscanf(fp, L"%ls%ls%u%d", state, capital, &population, &elevation);
        wprintf(L"State  : %ls\nCapital: %ls\nJackson population (in 2020): %u\n"
                L"Highest elevation: %dft\n",
                state, capital, population, elevation);
        fclose(fp);
    }
}

State: California
Age  : 170 years
Pi   : 3.14159
 
State  : Mississippi
Capital: Jackson
Jackson population (in 2020): 420000
Highest elevation: 807ft

References

• C11 standard (ISO/IEC 9899:2011):
• 7.29.2.2 The fwscanf function (p: 410-416)
• 7.29.2.4 The swscanf function (p: 417)
• 7.29.2.12 The wscanf function (p: 421)
• K.3.9.1.2 The fwscanf_s function (p: 628-629)
• K.3.9.1.5 The swscanf_s function (p: 631)
• K.3.9.1.14 The wscanf_s function (p: 638)
• C99 standard (ISO/IEC 9899:1999):
• 7.24.2.2 The fwscanf function (p: 356-362)
• 7.24.2.4 The swscanf function (p: 362)
• 7.24.2.12 The wscanf function (p: 366-367)

See also