PHP数组或字符串的性能和内存使用情况

Question

Option 1 or Option 2 which is the most feasible way in terms of memory and performance usage to append multiple email ids in the following loop.

Option 1: String $errorString

while (!feof($file_handle)) {  
    $errorString .= $email."<br>";
}

Option 2: Array $errorArray[]

while (!feof($file_handle)) {  
    $errorArray[].= $email."<br>";
}

Answer 1

The array will use a little more memory, because it needs to store all the strings and all the array elements that refer to them.

The string will take more time, because every time you concatenate it has to copy the both strings into the new value of $errorString .

Unless you have thousands of emails it's unlikely to make any noticeable difference, so you should use whichever method makes the rest of the code easier. Premature optimization is the root of all evil.

Answer 2

Well then. In most cases, the string would undergo minimal processing in the background to have to a append a substring to it. However, there are a few noticeable things there:

1. You will do some processing later with the string or array you create. If you are to display the email IDs to the user without individual formatting, then you'd probably display the string as it is without any further requirement. This also applies when you want to store the final result in a database or just anything that would just take the whole string. This would require you to first implode the array if you used the array then use the string, thus making the string the better alternative.

However, if you need to present these as separate fields, then you'd be required to first explode the string to the different portions before you can use them. Again, you would incur more memory usage if you used a string.

The point is, it depends with what you are going to do with the variable.

2. How big will the variable be? This is actually the most important issue. If you are going to have just a little content in the variable, say something below a thousand members, then your choice wouldn't really matter unless you would be doing something quite memory intensive with each of them. If you wouldn't be doing several million iterations, then I guess the difference in performance of the two would be negligible, which means the choice you make doesn't really matter.

PS: when you assign a varibale to array, you don't use array [] .= something as you did in the question. You do array[] = something since you are appending the something to array rather than to array[index] .