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@(#)vis.3 8.1 (Berkeley) 6/9/93
.Dd February 19, 2013 .Dt VIS 3 .Os .Sh NAME .Nm vis , .Nm nvis , .Nm strvis , .Nm strnvis , .Nm strvisx , .Nm strnvisx , .Nm strenvisx , .Nm svis , .Nm snvis , .Nm strsvis , .Nm strsnvis , .Nm strsvisx , .Nm strsnvisx , .Nm strsenvisx .Nd visually encode characters .Sh LIBRARY .Lb libc .Sh SYNOPSIS n vis.h .Ft char * .Fn vis "char *dst" "int c" "int flag" "int nextc" .Ft char * .Fn nvis "char *dst" "size_t dlen" "int c" "int flag" "int nextc" .Ft int .Fn strvis "char *dst" "const char *src" "int flag" .Ft int .Fn strnvis "char *dst" "size_t dlen" "const char *src" "int flag" .Ft int .Fn strvisx "char *dst" "const char *src" "size_t len" "int flag" .Ft int .Fn strnvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" .Ft int .Fn strenvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "int *cerr_ptr" .Ft char * .Fn svis "char *dst" "int c" "int flag" "int nextc" "const char *extra" .Ft char * .Fn snvis "char *dst" "size_t dlen" "int c" "int flag" "int nextc" "const char *extra" .Ft int .Fn strsvis "char *dst" "const char *src" "int flag" "const char *extra" .Ft int .Fn strsnvis "char *dst" "size_t dlen" "const char *src" "int flag" "const char *extra" .Ft int .Fn strsvisx "char *dst" "const char *src" "size_t len" "int flag" "const char *extra" .Ft int .Fn strsnvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "const char *extra" .Ft int .Fn strsenvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "const char *extra" "int *cerr_ptr" .Sh DESCRIPTION The .Fn vis function copies into .Fa dst a string which represents the character .Fa c . If .Fa c needs no encoding, it is copied in unaltered. The string is null terminated, and a pointer to the end of the string is returned. The maximum length of any encoding is four bytes (not including the trailing .Dv NUL ) ; thus, when encoding a set of characters into a buffer, the size of the buffer should be four times the number of bytes encoded, plus one for the trailing .Dv NUL . The flag parameter is used for altering the default range of characters considered for encoding and for altering the visual representation. The additional character, .Fa nextc , is only used when selecting the .Dv VIS_CSTYLE encoding format (explained below).
p The .Fn strvis , .Fn strnvis , .Fn strvisx , and .Fn strnvisx functions copy into .Fa dst a visual representation of the string .Fa src . The .Fn strvis and .Fn strnvis functions encode characters from .Fa src up to the first .Dv NUL . The .Fn strvisx and .Fn strnvisx functions encode exactly .Fa len characters from .Fa src (this is useful for encoding a block of data that may contain .Dv NUL Ns 's ) . Both forms .Dv NUL terminate .Fa dst . The size of .Fa dst must be four times the number of bytes encoded from .Fa src (plus one for the .Dv NUL ) . Both forms return the number of characters in .Fa dst (not including the trailing .Dv NUL ) . The .Dq Nm n versions of the functions also take an additional argument .Fa dlen that indicates the length of the .Fa dst buffer. If .Fa dlen is not large enough to fit the converted string then the .Fn strnvis and .Fn strnvisx functions return -1 and set .Va errno to .Dv ENOSPC . The .Fn strenvisx function takes an additional argument, .Fa 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.
p The functions .Fn svis , .Fn snvis , .Fn strsvis , .Fn strsnvis , .Fn strsvisx , .Fn strsnvisx , and .Fn strsenvisx correspond to .Fn vis , .Fn nvis , .Fn strvis , .Fn strnvis , .Fn strvisx , .Fn strnvisx , and .Fn strenvisx but have an additional argument .Fa extra , pointing to a .Dv NUL terminated list of characters. These characters will be copied encoded or backslash-escaped into .Fa dst . These functions are useful e.g. to remove the special meaning of certain characters to shells.
p The encoding is a unique, invertible representation composed entirely of graphic characters; it can be decoded back into the original form using the .Xr unvis 3 , .Xr strunvis 3 or .Xr strnunvis 3 functions.
p There are two parameters that can be controlled: the range of characters that are encoded (applies only to .Fn vis , .Fn nvis , .Fn strvis , .Fn strnvis , .Fn strvisx , and .Fn strnvisx ) , and the type of representation used. By default, all non-graphic characters, except space, tab, and newline are encoded (see .Xr isgraph 3 ) . The following flags alter this: l -tag -width VIS_WHITEX t Dv VIS_GLOB Also encode the magic characters .Ql ( * , .Ql ? , .Ql [ and .Ql # ) recognized by .Xr glob 3 . t Dv VIS_SP Also encode space. t Dv VIS_TAB Also encode tab. t Dv VIS_NL Also encode newline. t Dv VIS_WHITE Synonym for .Dv VIS_SP | .Dv VIS_TAB | .Dv VIS_NL . t Dv VIS_SAFE Only encode .Dq unsafe characters. Unsafe means control characters which may cause common terminals to perform unexpected functions. Currently this form allows space, tab, newline, backspace, bell, and return \(em in addition to all graphic characters \(em unencoded. .El
p (The above flags have no effect for .Fn svis , .Fn snvis , .Fn strsvis , .Fn strsnvis , .Fn strsvisx , and .Fn strsnvisx . When using these functions, place all graphic characters to be encoded in an array pointed to by .Fa extra . In general, the backslash character should be included in this array, see the warning on the use of the .Dv VIS_NOSLASH flag below).
p There are four forms of encoding. All forms use the backslash character .Ql \e to introduce a special sequence; two backslashes are used to represent a real backslash, except .Dv VIS_HTTPSTYLE that uses .Ql % , or .Dv VIS_MIMESTYLE that uses .Ql = . These are the visual formats: l -tag -width VIS_CSTYLE t (default) Use an .Ql M to represent meta characters (characters with the 8th bit set), and use caret .Ql ^ to represent control characters (see .Xr iscntrl 3 ) . The following formats are used: l -tag -width xxxxx t Dv \e^C Represents the control character .Ql C . Spans characters .Ql \e000 through .Ql \e037 , and .Ql \e177 (as .Ql \e^? ) . t Dv \eM-C Represents character .Ql C with the 8th bit set. Spans characters .Ql \e241 through .Ql \e376 . t Dv \eM^C Represents control character .Ql C with the 8th bit set. Spans characters .Ql \e200 through .Ql \e237 , and .Ql \e377 (as .Ql \eM^? ) . t Dv \e040 Represents .Tn ASCII space. t Dv \e240 Represents Meta-space. .El
p t Dv VIS_CSTYLE Use C-style backslash sequences to represent standard non-printable characters. The following sequences are used to represent the indicated characters: d -unfilled -offset indent .Li \ea Tn \(em BEL No (007) .Li \eb Tn \(em BS No (010) .Li \ef Tn \(em NP No (014) .Li \en Tn \(em NL No (012) .Li \er Tn \(em CR No (015) .Li \es Tn \(em SP No (040) .Li \et Tn \(em HT No (011) .Li \ev Tn \(em VT No (013) .Li \e0 Tn \(em NUL No (000) .Ed
p When using this format, the .Fa nextc parameter is looked at to determine if a .Dv NUL character can be encoded as .Ql \e0 instead of .Ql \e000 . If .Fa nextc is an octal digit, the latter representation is used to avoid ambiguity. t Dv VIS_OCTAL Use a three digit octal sequence. The form is .Ql \eddd where .Em d represents an octal digit. t Dv VIS_HTTPSTYLE Use URI encoding as described in RFC 1738. The form is .Ql %xx where .Em x represents a lower case hexadecimal digit. t Dv VIS_MIMESTYLE Use MIME Quoted-Printable encoding as described in RFC 2045, only don't break lines and don't handle CRLF. The form is .Ql =XX where .Em X represents an upper case hexadecimal digit. .El
p There is one additional flag, .Dv VIS_NOSLASH , which inhibits the doubling of backslashes and the backslash before the default format (that is, control characters are represented by .Ql ^C and meta characters as .Ql M-C ) . With this flag set, the encoding is ambiguous and non-invertible. .Sh MULTIBYTE CHARACTER SUPPORT These functions support multibyte character input. The encoding conversion is influenced by the setting of the .Ev LC_CTYPE environment variable which defines the set of characters that can be copied without encoding.
p When 8-bit data is present in the input, .Ev 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.
p
As noted above,
.Fa dst
must be four times the number of bytes processed from
.Fa src .
But note that each multibyte character can be up to
.Dv MB_LEN_MAX
bytes
(see
.Xr multibyte 3 )
so in terms of multibyte characters,
.Fa dst
must be four times
.Dv MB_LEN_MAX
times the number of characters processed from
.Fa src .
.Sh ENVIRONMENT
l -tag -width ".Ev LC_CTYPE" t Ev LC_CTYPE Specify the locale of the input data.
Set to C if the input data locale is unknown.
.El
.Sh ERRORS
The functions
.Fn nvis
and
.Fn snvis
will return
.Dv NULL
and the functions
.Fn strnvis ,
.Fn strnvisx ,
.Fn strsnvis ,
and
.Fn strsnvisx ,
will return -1 when the
.Fa dlen
destination buffer size is not enough to perform the conversion while
setting
.Va errno
to:
l -tag -width ".Bq Er ENOSPC" t Bq Er ENOSPC The destination buffer size is not large enough to perform the conversion.
.El
.Sh SEE ALSO
.Xr unvis 1 ,
.Xr vis 1 ,
.Xr glob 3 ,
.Xr multibyte 3 ,
.Xr unvis 3
.Rs
.%A T. Berners-Lee
.%T Uniform Resource Locators (URL)
.%O "RFC 1738"
.Re
.Rs
.%T "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"
.%O "RFC 2045"
.Re
.Sh HISTORY
The
.Fn vis ,
.Fn strvis ,
and
.Fn strvisx
functions first appeared in
x 4.4 . The
.Fn svis ,
.Fn strsvis ,
and
.Fn strsvisx
functions appeared in
.Nx 1.5
and
.Fx 9.2 .
The buffer size limited versions of the functions
o Fn nvis , .Fn strnvis , .Fn strnvisx , .Fn snvis , .Fn strsnvis , and .Fn strsnvisx Pc appeared in .Nx 6.0 and .Fx 9.2 . Myltibyte character support was added in .Nx 7.0 and .Fx 9.2 .