Php uses the for loop to generate a four-digit verification code that only generates three

I use phpfor to generate a verification code cyclically. I often find that a verification code fails to be generated. I hope you can help me with the Code. Thank you very much! {Code...} is generated

I use php for to generate a verification code repeatedly. I often find that one Verification Code fails to be generated. I hope you can help me with the Code. Thank you very much!

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I use php for to generate a verification code repeatedly. I often find that one Verification Code fails to be generated. I hope you can help me with the Code. Thank you very much!

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One possible reason

$ Fontcontent = substr ($ data, rand (0, strlen ($ data), 1 );

Change

$ Fontcontent = substr ($ data, rand (0, strlen ($ data)-1), 1 );

The reason is that the rand method of php is a closed interval, and both the first and last values are the minimum and maximum values.

Trystrlen($data)-1?

In$fontcontent = substr($data,rand(0,strlen($data)),1);This line

Emma did not reply when I clicked in. Similar to upstairs, I did not mean it.
Let's like it upstairs.