What is the difference between strlen and sizeof in the C language?

The strlen function is used to calculate the length of a string, which is the number of valid characters in the string excluding the null character ‘\0’ at the end of the string. On the other hand, the sizeof operator is used to determine the amount of memory occupied by a variable or data type, including both the size of the variable itself and the size of its data type. Therefore, strlen returns the length of the string, while sizeof returns the memory size occupied by a variable or data type.