Notes on PHP weak type safety issues

1. Type conversion problem

 <span style="color: #008080;">intval</span><span style="color: #000000;">();

 

    </span><span style="color: #008080;">var_dump</span>(<span style="color: #008080;">intval</span>('1asdfasd'));  <span style="color: #008000;">//</span><span style="color: #008000;">1</span>

    <span style="color: #008080;">var_dump</span>(<span style="color: #008080;">intval</span>('awqw12'));  <span style="color: #008000;">//</span><span style="color: #008000;">0</span>

    <span style="color: #008080;">var_dump</span>(<span style="color: #008080;">intval</span>(<span style="color: #0000ff;">array</span>()));    <span style="color: #008000;">//</span><span style="color: #008000;">0</span>

    <span style="color: #008080;">var_dump</span>(<span style="color: #008080;">intval</span>(<span style="color: #0000ff;">array</span>('foo','val'))); <span style="color: #008000;">//</span><span style="color: #008000;">1</span>

    <span style="color: #008080;">var_dump</span>(<span style="color: #008080;">intval</span>(0x1A)); <span style="color: #008000;">//</span><span style="color: #008000;">26  十六进制转换</span>

    <span style="color: #008080;">var_dump</span>(<span style="color: #008080;">intval</span>('asdfqwer')); <span style="color: #008000;">//</span><span style="color: #008000;">0</span>

   

intval If the converted value is a string, it will not return an error, but 0. If the converted value is an array, there are two situations. When the converted value is an empty array, it will return 0, otherwise it will return 1

Note: PHP uses 32-bit memory to store an integer. 32-bit can represent 4294967296 numbers. If there is a sign, it is -2147483647 to 2147483648;

2. The problem of looseness of built-in functions

 switch();

 

     $i='3adcd';

     switch($i){

              case 1:

                     echo 'i is 1';

                     break;

              case 2:

                     echo 'i is 2';

                     break;

              case 3:

                     echo 'i is 3';

                     break;

              default:

                    echo 'i is default';

                    break;

     }

The above result will enter switch case 3. Why is this happening? If the switch is a numeric type case, the switch will convert the parameters into the int class. Therefore, when the above is executed, $i will be processed first. Type conversion, the conversion result is 3, so. . .

  <span style="color: #008080;">in_array</span><span style="color: #000000;">();

    </span><span style="color: #800080;">$arr</span> = [0,1,2,3,'test'<span style="color: #000000;">];

    </span><span style="color: #008080;">var_dump</span>(<span style="color: #008080;">in_array</span>('abd',<span style="color: #800080;">$arr</span>));    <span style="color: #008000;">//</span><span style="color: #008000;"> true</span>

    <span style="color: #008080;">var_dump</span>(<span style="color: #008080;">in_array</span>('1bc',<span style="color: #800080;">$arr</span>));    <span style="color: #008000;">//</span><span style="color: #008000;"> true</span>

Why is the above execution result like this? After querying the manual, the official statement is that in_array defaults to a loose comparison method, which only compares whether the values ​​are equal, but does not compare whether the types of the values ​​are the same, so the above As a result, you can set the third parameter of the in_array function. Setting it to True is a strict comparison method.

The above are the things we need to pay attention to in our daily development.