Which string functions are in the C programming language?

Several commonly used string functions in the C language include:

1. strlen: a function used to determine the length of a string.
2. Strcpy is used to copy one string into another string.
3. strncpy is an function used to copy a portion of one string to another string.
4. strcat is a function used to append one string to the end of another.
5. strncat is used to concatenate a portion of one string to the end of another string.
6. strcmp is used to compare whether two strings are equal.
7. strncmp is used to compare whether a portion of two strings are equal.
8. strchr: used to find the position of the first occurrence of a specified character in a string.
9. strrchr: used to locate the last occurrence of a specified character in a string.
10. strstr is used to locate the first occurrence of one string within another string.
11. strtok: a function used to divide a string into multiple substrings.
12. sprintf: a function for writing formatted data to a string.
13. sscanf is used to read formatted data from a string.
14. memcpy is used to copy the contents of one memory area to another memory area.
15. memmove: Used to move the contents of a memory area to another.

The above are some commonly used string functions, there are other string functions that can be chosen based on actual needs.