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title TARGET DECK FILE TAGS tags
Strings Obsidian::STEM c17
c17

Overview

A contiguous sequence of characters terminated by the NUL character (refer to ascii). Text data is said to be more platform-independent than endianness data since it is unaffected by word size or byte ordering.

%%ANKI Basic What is a C-style string? Back: A character array terminated with a NUL character. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What character terminates all C-style strings? Back: NUL Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What is the decimal value of NUL in ASCII encoding? Back: 0 Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic Text is more platform-independent than e.g. integer encodings because it is unaffected by what two properties? Back: Word size and byte ordering. Reference: Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.

END%%

%%ANKI Basic What kind of array can be expressed as a literal? Back: Strings. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).

END%%

%%ANKI Cloze A {string} is a {NUL}-terminated array of {char}. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).

END%%

%%ANKI Cloze <string.h> uses prefix {mem} to refer to {array} arguments. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).

END%%

%%ANKI Cloze <string.h> uses prefix {str} to refer to {string} arguments. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).

END%%

Escape Sequences

C has a standard for processing different escape sequences. Many languages built with C in mind parse these escape sequences in a similar way.

  • \ooo: Consists of one to three octal digits.

%%ANKI Basic How are C escape sequences for octal digits denoted? Back: As \ooo. Reference: Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, 2nd ed (Englewood Cliffs, N.J: Prentice Hall, 1988).

END%%

%%ANKI Basic In C, \ooo allows specifying how many octal digits? Back: One to three. Reference: Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, 2nd ed (Englewood Cliffs, N.J: Prentice Hall, 1988).

END%%

%%ANKI Basic How are C escape sequences exposed in bash? Back: Using ANSI-C quoting, i.e. $$'string'. Reference: Mendel Cooper, “Advanced Bash-Scripting Guide,” n.d., 916. Tags: bash

END%%

  • \xhh: Consists of one or more radices#Hexadecimal digits. The x prefix is required to distinguish from octal escape sequences.
    • bash/index supports this sequence as $'\xhh'. One or two digits is supported.

%%ANKI Basic How are C escape sequences for hexadecimal digits denoted? Back: As \xhh. Reference: Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, 2nd ed (Englewood Cliffs, N.J: Prentice Hall, 1988).

END%%

%%ANKI Basic In C, \x allows specifying how many hexadecimal digits? Back: One or more. Reference: Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, 2nd ed (Englewood Cliffs, N.J: Prentice Hall, 1988).

END%%

%%ANKI Basic What footgun does C's \x sequence expose? Back: Using more than two hexadecimal digits can produce undefined results. Reference: Arnold D. Robbins, “GAWK: Effective AWK Programming,” October 2023, https://www.gnu.org/software/gawk/manual/gawk.pdf.

END%%

  • \uhhhh: Introduced in C11 to represent Unicode code points. Must have exactly four hexadecimal characters specified with 0 leading padding if necessary.
    • bash/index supports this sequence as $'uhhhh'. One to four hex digits is supported.

%%ANKI Basic What two ways are C escape sequences for unicode denoted? Back: As \uhhhh or \Uhhhhhhhh. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020). Tags: encoding::unicode

END%%

%%ANKI Basic In C, \u allows specifying how many hexadecimal digits? Back: Exactly four. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020). Tags: encoding::unicode

END%%

%%ANKI Basic In what standard were C's \u and \U escape sequences introduced? Back: C11. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020). Tags: encoding::unicode

END%%

  • \Uhhhhhhhh: Introduced in C11 to represent larger unicode code points. Must have exactly eight hexadecimal characters specified with 0 leading padding if necessary.

%%ANKI Basic In C, \U allows specifying how many hexadecimal digits? Back: Exactly eight. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020). Tags: encoding::unicode

END%%

%%ANKI Basic Why does C have both \u and \U? Back: \U accommodates for larger code point values. Reference: Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020). Tags: encoding::unicode

END%%

Copying Functions

The two primary functions used for copying memory are memcpy and memmove:

void* memcpy(void* restrict s1, const void* restrict s2, size_t n);
void* memmove(void* s1, const void* s2, size_t n);

%%ANKI Basic What are the two primary functions provided by the standard library for copying memory? Back: memcpy and memmove. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What is the function prototype of memcpy? Back:

void* memcpy(void* restrict s1, const void* restrict s2, size_t n);

Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the memcpy function do? Back: Copies a specified number of bytes from one object to another. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic Disregarding out of bounds errors, when does memcpy invoke undefined behavior? Back: When copying occurs between objects that overlap in memory. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the first argument of memcpy refer to? Back: The destination address bytes are copied to. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the second argument of memcpy refer to? Back: The source address bytes are copied from. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the third argument of memcpy refer to? Back: The number of bytes to copy from the source address. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic Which of memcpy or memmove is faster? Back: memcpy Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic Why is memmove slower than memcpy? Back: It's implemented as if copying first into a temporary array that does not overlap the arguments in memory. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic When should you prefer using memcpy instead of memmove? Back: When the copying occurs between objects that do not overlap in memory. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic Which standard header library defines memcpy? Back: <string.h> Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What is the function prototype of memmove? Back:

void* memmove(void* s1, const void* s2, size_t n);

Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the first argument of memmove refer to? Back: The destination address bytes are copied to. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the second argument of memmove refer to? Back: The source address bytes are copied from. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the third argument of memmove refer to? Back: The number of bytes to copy from the source address. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic Disregarding out of bounds errors, when does memmove invoke undefined behavior? Back: N/A. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic When should you prefer using memmove instead of memcopy? Back: When the copying occurs between objects that overlap in memory. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic Which standard header library defines memmove? Back: <string.h> Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

%%ANKI Basic What does the memmove function do? Back: Copies a specified number of bytes from one object to another. Reference: “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.

END%%

Bibliography

  • Arnold D. Robbins, “GAWK: Effective AWK Programming,” October 2023, https://www.gnu.org/software/gawk/manual/gawk.pdf.
  • Brian W. Kernighan and Dennis M. Ritchie, The C Programming Language, 2nd ed (Englewood Cliffs, N.J: Prentice Hall, 1988).
  • Bryant, Randal E., and David O'Hallaron. Computer Systems: A Programmer's Perspective. Third edition, Global edition. Always Learning. Pearson, 2016.
  • “ISO: Programming Languages - C17,” April 2017, https://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf.
  • Jens Gustedt, Modern C (Shelter Island, NY: Manning Publications Co, 2020).
  • Mendel Cooper, “Advanced Bash-Scripting Guide,” n.d., 916.