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For character strings, the standard library uses the convention that strings are null-terminated: a string of n characters is represented as an array of n + 1 elements, the last of which is a "NUL character" with numeric value 0.
For example, the null character (U+0000 NULL) is used in C-programming application environments to indicate the end of a string of characters. In this way, these programs only require a single starting memory address for a string (as opposed to a starting address and a length), since the string ends once the program reads the null character.
A one byte offset, such as the hexadecimal ASCII value of a character (e.g. X'29') can be used to point to an alternative integer value (or index) in an array (e.g., X'01'). In this way, characters can be very efficiently translated from 'raw data' to a usable sequential index and then to an absolute address without a lookup table.
In all modern character sets, the null character has a code point value of zero. In most encodings, this is translated to a single code unit with a zero value. For instance, in UTF-8 it is a single zero byte. However, in Modified UTF-8 the null character is encoded as two bytes : 0xC0,0x80. This allows the byte with the value of zero, which is ...
Similarly, if the numeric character reference ð appears in element content, it will be interpreted as the single Unicode character 00F0 (small letter eth). But if the same appears in a CDATA section, it will be parsed as six characters: ampersand, hash mark, digit 2, digit 4, digit 0, semicolon.
In CP/M, 86-DOS, MS-DOS, PC DOS, DR-DOS, and their various derivatives, the SUB character was also used to indicate the end of a character stream, [citation needed] and thereby used to terminate user input in an interactive command line window (and as such, often used to finish console input redirection, e.g. as instigated by the command COPY ...
Off-by-one errors are common in using the C library because it is not consistent with respect to whether one needs to subtract 1 byte – functions like fgets() and strncpy will never write past the length given them (fgets() subtracts 1 itself, and only retrieves (length − 1) bytes), whereas others, like strncat will write past the length given them.
In computer programming, a null-terminated string is a character string stored as an array containing the characters and terminated with a null character (a character with an internal value of zero, called "NUL" in this article, not same as the glyph zero).