Some uncommon problems in php foreach/in_array, foreachin_array_PHP tutorial

Some uncommon problems in PHP foreach/in_array, foreachin_array

PHP is very efficient in development, which is understandable, but it sacrifices execution efficiency. The php array function is very powerful, but you should also consider it more and try several situations just in case. Here, I will briefly mention the two pitfalls encountered. If more are found in the future, I will add them. !

　foreach provides a simple way to traverse an array, which can easily read the contents of data or objects. However, the official documentation says that since foreach relies on the internal array pointer, Modifying its value within a loop may cause unexpected behavior. So, basically, 1. Don't try to modify the value inside the loop, otherwise the result will be beyond what you want; 2. Using '&' is a safe way, although it is rarely used, but when it is used, After the reference ends, the unset function should be called immediately to destroy the variable. Otherwise, if this variable is used again in the following code, the last value of the loop will be modified, thus obtaining an unexpected value. For example: when the list is looped out, there will be many messy values ​​or null values ​​in the last line of output. Using unset solves this problem.

in_array, its meaning is to check whether the previous string exists in the following array, and in most cases, it also works like this, but when the following array is an integer, such as array(0,1,2 , 3), there is a problem. PHP will intval the previous string, so that the value 0 will be obtained. Then if by chance, your array has this value, then the equation will be established. Is it beyond the limit? What about expectations? Therefore, when it is determined that the following data is an integer, especially if it may be 0 (this may replace all strings), you must not use this function anymore. You can use key_exists instead, but the following data You need to use array_flip to perform the inversion operation.

What happens when a string is used as an array to get values? PHP is a very fault-tolerant language. It will try its best to help you correct your mistakes, so it smartly converts your reference subscript into an integer. Of course, you get 0. Then the string subscript is 0 and the value is You will get the value of the first string. Is it beyond your expectation? The solution is to confirm whether the variable is an array before referencing the subscript, is_array.

Although there are many seniors who have encountered this or that problem and kept talking about it, we are still inevitable and keep making mistakes after all. Maybe this is society! Everyone is so busy, how can we have time to crack your crappy code! Haha

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