Strcpy(p, p 1) copies the string.
Strncpy(p, p 1, n) copies a string of a specified length.
Strcat(p, p 1) additional string
Strncat(p, p 1, n) appends a string with a specified length.
Strlen(p) takes the length of the string.
Strcmp(p, p 1) comparison string
Strcasecmp ignores case comparison strings.
Strncmp(p, p 1, n) compares strings of a specified length.
Strchr(p, c) looks for the specified character in the string.
Strrchr(p, c) looks up the string in reverse.
Strstr(p, p 1) looks for a string.
Strpbrk(p, p 1) takes all the characters of the target string as a set, and looks for any element of the set in the current string.
Strspn(p, p 1) takes all the characters of the target string as a set, and finds the offset of any element that does not belong to the set in the current string.
Strcspn(p, p 1) takes all the characters of the target string as a set, and finds the offset of any element belonging to the set in the current string.
* A string handler with a specified length fills a zero terminator after the processed string.
2) Conversion from character string to numeric type
Strtod(p, ppend) converts the string p into a double value, and stores the subsequent string pointer in the char* type storage pointed by ppend.
Strotol (p, ppend, base) converts the string p into an integer value of type long, and base explicitly sets the converted integer system. If it is set to 0, the system used is judged according to a specific format. 0X, 0x prefix is interpreted as an integer in hexadecimal format, and 0 prefix is interpreted as an integer in octal format.
Atoi(p) string is converted to int integer.
Atof(p) strings are converted into double symbol points.
Atol(p) string is converted to a long integer.
3) Character checking
Isalpha () checks whether it is an alphabetic character.
Isupper () checks whether it is an uppercase character.
Islower () checks whether it is a lowercase alphabetic character.
Isdig () checks whether it is a number.
Isxdigit () checks whether it is a valid character represented by hexadecimal digits.
Isspace () checks whether it is a space type character.
Iscntrl () checks whether it is a control character.
Isfunction () checks whether it is punctuation.
Isalnum () checks letters and numbers.
Isprint () checks whether it is a printable character.
Isgraph () checks whether it is a graphic character, which is equivalent to isalnum () | ispact ().