In computing, a C string is a character sequence stored as a one-dimensional character array and terminated with a null character ('\0', called NUL in ASCII). The name refers to the ubiquitous C programming language which uses this string representation.
In the C++ programming language, C strings are used in addition to another representation of character sequences, the std::string container found in the Standard Template Library (STL). Thus, it is important to differentiate between the traditional "C strings" and the more sophisticated "string" objects provided by the STL.
The null-termination characteristic has historically created security problems related to the length of the string. If the null character is not correctly accounted for, any following non-related memory area may also be processed as a part of the character sequence. This can lead to program crashes or leakage of program internal information to attackers or non-understanding users.
C String header
The <cstring> header and its functions are the ideal way to work with C strings. Typical operator use with C strings will frequently create problems with pointers. As an example, using the = operator between two C strings does not copy the values in the array but copies a pointer to the array. This is incorrect usage for most typical applications.
Example:
To copy a C string correctly, the following format could be used
memcpy(CstringDst, CstringSrc, strlen(CstringSrc) + 1);
Where CstringDst is the destination C string to be copied into and CstringSrc is the source of the C string. The last argument will set the length of the destination C array. It will set this length to the length of the source plus 1 to account for the terminating character.
The functions included in <cstring> are as follows:
Copying:
memcpy Copies a block of memory
memmove Move block of memory
strcpy Copy string
strncpy Copy characters from string
Concatenation:
strcat Concatenate strings
strncat Append characters from string
Comparison:
memcmp Compare two blocks of memory
strcmp Compare two strings
strcoll Compare two strings using locale
strncmp Compare characters of two strings
strxfrm Transform string using locale
Searching:
memchr Locate character in block of memory
strchr Locate first occurrence of character in string
strcspn Get span until character in string
strpbrk Locate character in string
strrchr Locate last occurrence of character in string
strspn Get span of character set in string
strstr Locate substring
strtok Split string into tokens
Other:
memset Fill block of memory
strerror Get pointer to error message string
strlen Get string length
Trivia
C strings are exactly equivalent to the strings created by the .ASCIZ directive implemented by the PDP-11 and VAX macroassembly languages.