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Diffstat (limited to 'manual/string.texi')
| -rw-r--r-- | manual/string.texi | 81 |
1 files changed, 72 insertions, 9 deletions
diff --git a/manual/string.texi b/manual/string.texi index 9d242b7..8f09ac9 100644 --- a/manual/string.texi +++ b/manual/string.texi @@ -32,9 +32,10 @@ too. * Search Functions:: Searching for a specific element or substring. * Finding Tokens in a String:: Splitting a string into tokens by looking for delimiters. +* Encode Binary Data:: Encoding and Decoding of Binary Data. @end menu -@node Representation of Strings, String/Array Conventions, , String and Array Utilities +@node Representation of Strings @section Representation of Strings @cindex string, representation of @@ -99,7 +100,7 @@ checks for overflowing the array. Many of the library functions an extra byte to hold the null character that marks the end of the string. -@node String/Array Conventions, String Length, Representation of Strings, String and Array Utilities +@node String/Array Conventions @section String and Array Conventions This chapter describes both functions that work on arbitrary arrays or @@ -132,7 +133,7 @@ other hand, when you are manipulating null-terminated strings it is usually more convenient to use the @samp{str} functions, unless you already know the length of the string in advance. -@node String Length, Copying and Concatenation, String/Array Conventions, String and Array Utilities +@node String Length @section String Length You can get the length of a string using the @code{strlen} function. @@ -166,7 +167,7 @@ strlen (string) @end smallexample @end deftypefun -@node Copying and Concatenation, String/Array Comparison, String Length, String and Array Utilities +@node Copying and Concatenation @section Copying and Concatenation You can use the functions described in this section to copy the contents @@ -470,7 +471,7 @@ BSD. Note that it is not as general as @code{memset}, because the only value it can store is zero. @end deftypefun -@node String/Array Comparison, Collation Functions, Copying and Concatenation, String and Array Utilities +@node String/Array Comparison @section String/Array Comparison @cindex comparing strings and arrays @cindex string comparison functions @@ -613,7 +614,7 @@ strncmp ("hello, world", "hello, stupid world!!!", 5) This is an obsolete alias for @code{memcmp}, derived from BSD. @end deftypefun -@node Collation Functions, Search Functions, String/Array Comparison, String and Array Utilities +@node Collation Functions @section Collation Functions @cindex collating strings @@ -792,9 +793,9 @@ sort_strings_fast (char **array, int nstrings) @end smallexample @strong{Compatibility Note:} The string collation functions are a new -feature of @w{ISO C}. Older C dialects have no equivalent feature. +feature of @w{ISO C 89}. Older C dialects have no equivalent feature. -@node Search Functions, Finding Tokens in a String, Collation Functions, String and Array Utilities +@node Search Functions @section Search Functions This section describes library functions which perform various kinds @@ -940,7 +941,7 @@ strpbrk ("hello, world", " \t\n,.;!?") @c @end group @end deftypefun -@node Finding Tokens in a String, , Search Functions, String and Array Utilities +@node Finding Tokens in a String @section Finding Tokens in a String @cindex tokenizing strings @@ -1087,3 +1088,65 @@ token = strsep (&running, delimiters); /* token => "and" */ token = strsep (&running, delimiters); /* token => "punctuation" */ token = strsep (&running, delimiters); /* token => NULL */ @end smallexample + +@node Encode Binary Data +@section Encode Binary Data + +To store or transfer binary data in environments which only support text +one has to encode the binary data by mapping the input bytes to +characters in the range allowed for storing or transfering. SVID +systems (and nowadays XPG compliant systems) have such a function in the +C library. + +@comment stdlib.h +@comment XPG +@deftypefun {char *} l64a (long int @var{n}) +This function encodes an input value with 32 bits using characters from +the basic character set. Groups of 6 bits are encoded using the +following table: + +@multitable {xxxxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} {xxx} +@item @tab 0 @tab 1 @tab 2 @tab 3 @tab 4 @tab 5 @tab 6 @tab 7 +@item 0 @tab @code{.} @tab @code{/} @tab @code{0} @tab @code{1} + @tab @code{2} @tab @code{3} @tab @code{4} @tab @code{5} +@item 8 @tab @code{6} @tab @code{7} @tab @code{8} @tab @code{9} + @tab @code{A} @tab @code{B} @tab @code{C} @tab @code{D} +@item 16 @tab @code{E} @tab @code{F} @tab @code{G} @tab @code{H} + @tab @code{I} @tab @code{J} @tab @code{K} @tab @code{L} +@item 24 @tab @code{M} @tab @code{N} @tab @code{O} @tab @code{P} + @tab @code{Q} @tab @code{R} @tab @code{S} @tab @code{T} +@item 32 @tab @code{U} @tab @code{V} @tab @code{W} @tab @code{X} + @tab @code{Y} @tab @code{Z} @tab @code{a} @tab @code{b} +@item 40 @tab @code{c} @tab @code{d} @tab @code{e} @tab @code{f} + @tab @code{g} @tab @code{h} @tab @code{i} @tab @code{j} +@item 48 @tab @code{k} @tab @code{l} @tab @code{m} @tab @code{n} + @tab @code{o} @tab @code{p} @tab @code{q} @tab @code{r} +@item 56 @tab @code{s} @tab @code{t} @tab @code{u} @tab @code{v} + @tab @code{w} @tab @code{x} @tab @code{y} @tab @code{z} +@end multitable + +The function returns a pointer to a static buffer which contains the +string representing of the encoding of @var{n}. To encoded a series of +bytes the use should append the new string to the destination buffer. +@emph{Warning:} Since a static buffer is used this function should not +be used in multi-threaded programs. There is no thread-safe alternatice +to this function in the C library. +@end deftypefun + +To decode data produced with @code{l64a} the following function should be +used. + +@deftypefun {long int} a64l (const char *@var{string}) +The parameter @var{string} should contain a string which was produced by +a call to @code{l64a}. The function processes the next 6 characters and +decodes the characters it finds according to the table above. +Characters not in the conversion table are simply ignored. This is +useful for breaking the information in lines in which case the end of +line characters are simply ignored. + +The decoded number is returned at the end as a @code{long int} value. +Consecutive calls to this function are possible but the caller must make +sure the buffer pointer is update after each call to @code{a64l} since +this function does not modify the buffer pointer. Every call consumes 6 +characters. +@end deftypefun |