# Null-terminated byte strings

From cppreference.com
< c‎ | string

A null-terminated byte string (NTBS) is a sequence of nonzero bytes followed by a byte with value zero (the terminating null character). Each byte in a byte string encodes one character of some character set. For example, the character array {'\x63','\x61','\x74','\0'} is an NTBS holding the string "cat" in ASCII encoding.

### Functions

##### Character classification

Defined in header `<ctype.h>`
isalnum | checks if a character is alphanumeric (function)
isalpha | checks if a character is alphabetic (function)
islower | checks if a character is lowercase (function)
isupper | checks if a character is an uppercase character (function)
isdigit | checks if a character is a digit (function)
isxdigit | checks if a character is a hexadecimal character (function)
iscntrl | checks if a character is a control character (function)
isgraph | checks if a character is a graphical character (function)
isspace | checks if a character is a space character (function)
isblank (C99) | checks if a character is a blank character (function)
isprint | checks if a character is a printing character (function)
ispunct | checks if a character is a punctuation character (function)

##### Character manipulation

tolower | converts a character to lowercase (function)
toupper | converts a character to uppercase (function)

Note: additional functions whose names begin with either `to` or `is`, followed by a lowercase letter, may be added to the header `ctype.h` in future and should not be defined by programs that include that header.

ASCII values (hex) | characters | `iscntrl` `iswcntrl` | `isprint` `iswprint` | `isspace` `iswspace` | `isblank` `iswblank` | `isgraph` `iswgraph` | `ispunct` `iswpunct` | `isalnum` `iswalnum` | `isalpha` `iswalpha` | `isupper` `iswupper` | `islower` `iswlower` | `isdigit` `iswdigit` | `isxdigit` `iswxdigit`
--- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | --- | ---
0 - 8 | `0x00-0x08` | control codes (`NUL`, etc.) | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
9 | `0x09` | tab (`\t`) | `≠0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
10 - 13 | `0x0A-0x0D` | whitespaces (`\n`,`\v`,`\f`,`\r`) | `≠0` | `0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
14 - 31 | `0x0E-0x1F` | control codes | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
32 | `0x20` | space | `0` | `≠0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`
33 - 47 | `0x21-0x2F` | `!"#$%&'()*+,-./` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
48 - 57 | `0x30-0x39` | `0123456789` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `0` | `0` | `0` | `≠0` | `≠0`
58 - 64 | `0x3a-0x40` | `:;<=>?@` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
65 - 70 | `0x41-0x46` | `ABCDEF` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `≠0` | `0` | `0` | `≠0`
71 - 90 | `0x47-0x5A` | `GHIJKLMNOPQRSTUVWXYZ` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `≠0` | `0` | `0` | `0`
91 - 96 | `0x5B-0x60` | `[\]^_`` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
97 -102 | `0x61-0x66` | `abcdef` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `0` | `≠0` | `0` | `≠0`
103-122 | `0x67-0x7A` | `ghijklmnopqrstuvwxyz` | `0` | `≠0` | `0` | `0` | `≠0` | `0` | `≠0` | `≠0` | `0` | `≠0` | `0` | `0`
123-126 | `0x7B-0x7E` | `{|}~` | `0` | `≠0` | `0` | `0` | `≠0` | `≠0` | `0` | `0` | `0` | `0` | `0` | `0`
127 | `0x7F` | backspace character (`DEL`) | `≠0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0` | `0`

##### Conversions to numeric formats

Defined in header `<stdlib.h>`
atof | converts a byte string to a floating-point value (function)
atoi atol atoll (C99) | converts a byte string to an integer value (function)
strtol strtoll (C99) | converts a byte string to an integer value (function)
strtoul strtoull (C99) | converts a byte string to an unsigned integer value (function)
strtof strtod strtold (C99)(C99) | converts a byte string to a floating point value (function)
Defined in header `<inttypes.h>`
strtoimax strtoumax (C99)(C99) | converts a byte string to intmax_t or uintmax_t (function)

##### String manipulation

Defined in header `<string.h>`
strcpy strcpy_s (C11) | copies one string to another (function)
strncpy strncpy_s (C11) | copies a certain amount of characters from one string to another (function)
strcat strcat_s (C11) | concatenates two strings (function)
strncat strncat_s (C11) | concatenates a certain amount of characters of two strings (function)
strxfrm | transform a string so that strcmp would produce the same result as strcoll (function)

##### String examination

Defined in header `<string.h>`
strlen strnlen_s (C11) | returns the length of a given string (function)
strcmp | compares two strings (function)
strncmp | compares a certain amount of characters of two strings (function)
strcoll | compares two strings in accordance to the current locale (function)
strchr | finds the first occurrence of a character (function)
strrchr | finds the last occurrence of a character (function)
strspn | returns the length of the maximum initial segment that consists of only the characters found in another byte string (function)
strcspn | returns the length of the maximum initial segment that consists of only the characters not found in another byte string (function)
strpbrk | finds the first location of any character in one string, in another string (function)
strstr | finds the first occurrence of a substring of characters (function)
strtok strtok_s (C11) | finds the next token in a byte string (function)

##### Character array manipulation

Defined in header `<string.h>`
memchr | searches an array for the first occurrence of a character (function)
memcmp | compares two buffers (function)
memset memset_s (C11) | fills a buffer with a character (function)
memcpy memcpy_s (C11) | copies one buffer to another (function)
memmove memmove_s (C11) | moves one buffer to another (function)

##### Miscellaneous

Defined in header `<string.h>`
strerror strerror_s strerrorlen_s (C11)(C11) | returns a text version of a given error code (function)

### References

- C11 standard (ISO/IEC 9899:2011):

  - 7.4 Character handling <ctype.h> (p: 200-204)

  - 7.8 Format conversion of integer types <inttypes.h> (p: 217-220)

  - 7.22 General utilities <stdlib.h> (p: 340-360)

  - 7.24 String handling <string.h> (p: 362-372)

  - 7.31.2 Character handling <ctype.h> (p: 455)

  - 7.31.5 Format conversion of integer types <inttypes.h> (p: 455)

  - 7.31.12 General utilities <stdlib.h> (p: 456)

  - 7.31.13 String handling <string.h> (p: 456)

  - K.3.6 General utilities <stdlib.h> (p: 604=613)

  - K.3.7 String handling <string.h> (p: 614-623)

- C99 standard (ISO/IEC 9899:1999):

  - 7.4 Character handling <ctype.h> (p: 181-185)

  - 7.8 Format conversion of integer types <inttypes.h> (p: 198-201)

  - 7.20 General utilities <stdlib.h> (p: 306-324)

  - 7.21 String handling <string.h> (p: 325-334)

  - 7.26.2 Character handling <ctype.h> (p: 401)

  - 7.26.4 Format conversion of integer types <inttypes.h> (p: 401)

  - 7.26.10 General utilities <stdlib.h> (p: 402)

  - 7.26.11 String handling <string.h> (p: 402)

- C89/C90 standard (ISO/IEC 9899:1990):

  - 4.3 CHARACTER HANDLING <ctype.h>

  - 4.10 GENERAL UTILITIES <stdlib.h>

  - 4.11 STRING HANDLING <string.h>

  - 4.13.2 Character handling <ctype.h>

  - 4.13.7 General utilities <stdlib.h>

  - 4.13.8 String handling <string.h>

### See also

C++ documentation for Null-terminated byte strings

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