In actual program development, performing string replacement operations is a very common task, and the use of the `str_replace` function will also be very frequent. Recently, while reading the book *PHP and MySQL Web Development*, I came across an explanation of the `str_replace` function. A small tip mentioned that arrays can be used as inputs for all three parameters of `str_replace`, but the explanation was rather brief. Therefore, I decided to experiment with the function to observe its behavior when arrays are passed into each parameter.
Function prototype: `mixed str_replace(mixed needle, mixed new_needle, mixed haystack[, int &count])`.
- `needle`: The string to be replaced.
- `new_needle`: The string used for replacement.
- `haystack`: The target string to operate on.
- `count`: The number of replacements performed (optional parameter).