VIS(3) | Library Functions Manual | VIS(3) |
char *
vis(char *dst, int c, int flag, int nextc);
char *
nvis(char *dst, size_t dlen, int c, int flag, int nextc);
int
strvis(char *dst, const char *src, int flag);
int
strnvis(char *dst, size_t dlen, const char *src, int flag);
int
strvisx(char *dst, const char *src, size_t len, int flag);
int
strnvisx(char *dst, size_t dlen, const char *src, size_t len, int flag);
int
strenvisx(char *dst, size_t dlen, const char *src, size_t len, int flag, int *cerr_ptr);
char *
svis(char *dst, int c, int flag, int nextc, const char *extra);
char *
snvis(char *dst, size_t dlen, int c, int flag, int nextc, const char *extra);
int
strsvis(char *dst, const char *src, int flag, const char *extra);
int
strsnvis(char *dst, size_t dlen, const char *src, int flag, const char *extra);
int
strsvisx(char *dst, const char *src, size_t len, int flag, const char *extra);
int
strsnvisx(char *dst, size_t dlen, const char *src, size_t len, int flag, const char *extra);
int
strsenvisx(char *dst, size_t dlen, const char *src, size_t len, int flag, const char *extra, int *cerr_ptr);
The strvis(), strnvis(), strvisx(), and strnvisx() functions copy into dst a visual representation of the string src. The strvis() and strnvis() functions encode characters from src up to the first NUL. The strvisx() and strnvisx() functions encode exactly len characters from src (this is useful for encoding a block of data that may contain NUL's). Both forms NUL terminate dst. The size of dst must be four times the number of bytes encoded from src (plus one for the NUL). Both forms return the number of characters in dst (not including the trailing NUL). The “n” versions of the functions also take an additional argument dlen that indicates the length of the dst buffer. If dlen is not large enough to fit the converted string then the strnvis() and strnvisx() functions return -1 and set errno to ENOSPC. The strenvisx() function takes an additional argument, cerr_ptr, that is used to pass in and out a multibyte conversion error flag. This is useful when processing single characters at a time when it is possible that the locale may be set to something other than the locale of the characters in the input data.
The functions svis(), snvis(), strsvis(), strsnvis(), strsvisx(), strsnvisx(), and strsenvisx() correspond to vis(), nvis(), strvis(), strnvis(), strvisx(), strnvisx(), and strenvisx() but have an additional argument extra, pointing to a NUL terminated list of characters. These characters will be copied encoded or backslash-escaped into dst. These functions are useful e.g. to remove the special meaning of certain characters to shells.
The encoding is a unique, invertible representation composed entirely of graphic characters; it can be decoded back into the original form using the unvis(3), strunvis(3) or strnunvis(3) functions.
There are two parameters that can be controlled: the range of characters that are encoded (applies only to vis(), nvis(), strvis(), strnvis(), strvisx(), and strnvisx()), and the type of representation used. By default, all non-graphic characters, except space, tab, and newline are encoded (see isgraph(3)). The following flags alter this:
*
’, ‘?
’, ‘[
’ and ‘#
’) recognized by glob(3).(The above flags have no effect for svis(), snvis(), strsvis(), strsnvis(), strsvisx(), and strsnvisx(). When using these functions, place all graphic characters to be encoded in an array pointed to by extra. In general, the backslash character should be included in this array, see the warning on the use of the VIS_NOSLASH flag below).
There are four forms of encoding. All forms use the backslash character ‘\
’ to introduce a special sequence; two backslashes are used to represent a real backslash, except VIS_HTTPSTYLE that uses ‘%
’, or VIS_MIMESTYLE that uses ‘=
’. These are the visual formats:
M
’ to represent meta characters (characters with the 8th bit set), and use caret ‘^
’ to represent control characters (see iscntrl(3)). The following formats are used:C
’. Spans characters ‘\000
’ through ‘\037
’, and ‘\177
’ (as ‘\^?
’).C
’ with the 8th bit set. Spans characters ‘\241
’ through ‘\376
’.C
’ with the 8th bit set. Spans characters ‘\200
’ through ‘\237
’, and ‘\377
’ (as ‘\M^?
’).
\a
— BEL (007)\b
— BS (010)\f
— NP (014)\n
— NL (012)\r
— CR (015)\s
— SP (040)\t
— HT (011)\v
— VT (013)\0
— NUL (000)
When using this format, the nextc parameter is looked at to determine if a NUL character can be encoded as ‘\0
’ instead of ‘\000
’. If nextc is an octal digit, the latter representation is used to avoid ambiguity.
\ddd
’ where d represents an octal digit.%xx
’ where x represents a lower case hexadecimal digit.=XX
’ where X represents an upper case hexadecimal digit.
There is one additional flag, VIS_NOSLASH, which inhibits the doubling of backslashes and the backslash before the default format (that is, control characters are represented by ‘^C
’ and meta characters as ‘M-C
’). With this flag set, the encoding is ambiguous and non-invertible.
When 8-bit data is present in the input, LC_CTYPE must be set to the correct locale or to the C locale. If the locales of the data and the conversion are mismatched, multibyte character recognition may fail and encoding will be performed byte-by-byte instead.
As noted above, dst must be four times the number of bytes processed from src. But note that each multibyte character can be up to MB_LEN_MAX bytes so in terms of multibyte characters, dst must be four times MB_LEN_MAX times the number of characters processed from src.
T. Berners-Lee, Uniform Resource Locators (URL), RFC 1738.
Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, RFC 2045.
February 19, 2013 | NetBSD 7.2 |