Fatal error: Call to undefined function_PHP教程

Fatal Errors in PHP Common Error Handling (1)----Function is not defined

1. Error type: PHP fatal error

Error type: PHP Fatal error

Fatal error: Call to undefined function (a) in (b) on line (c)

2. Error description:

This error report indicates that you are trying to call an undefined function, where

a---- represents an undefined function name;

b----The path where this script appears;

c----The line number where an undefined function is attempted to be called.

d----The line number when the function is defined for the second time.

3. Reasons and solutions:

Reason 1: You did not declare the function. For example, call the following function directly

myFunction();// There is no such function here

The results are as follows

Fatal error:Call to undefinedfunction myFunction()in(path) on line 1

Solution:

Check carefully whether this function is declared in your program.

Cause 2: The name you use when declaring the function is different from the name you use when calling it, such as

function myFunction(){// do something}myFuntion();// There is one less letter C

Solution: This is the most common mistake that many beginners make. Sometimes, because of underwriting, overwriting, or a wrong letter, it cannot be checked for a long time.

Cause 3: The error occurred when you called the new version of PHP built-in functions under the old version of PHP. Because this PHP built-in function does not exist at all in your old version. For example, you call mime_content_type()

in an old version of PHP

Fatal error:Call to undefinedfunction mime_content_type()

Solution: Open the PHP manual and carefully check which versions of PHP the built-in functions you are using are applicable to. Detailed version restrictions are noted for each built-in function in the PHP manual. For example (PHP 4 >= 4.3.0, PHP 5). Therefore, the solution is to upgrade your PHP version, or change to other built-in functions of the same type.

Cause 4: Your calling code for the function is written in a file different from the function declaration. For example, you wrote code like this in a.php file

myFunction();

And your function declaration is in b.php

function myFunction(){// do something}

Solution: This situation usually happens to PHP beginners. They forget that PHP does not automatically associate or reference files when calling functions. In other words, in the above situation, a.php and b.php will not have any relationship at all. At this time you need to use functions such as include() to associate the two.

Reason 5: Your calling code for the function is written in a file different from the function declaration, and you also introduced the file. But your function calling code is before the import file code. For example, you perform function calls in a.php and declare functions in b.php

a.php code

myFunction();include('b.php');

b.php code

function myFunction(){ echo '123';}

Solution: Like the above code, an error will be reported when executed. Because PHP cannot find the declaration of the function when executing the function call. Therefore, never write function calls before the function declaration file is introduced. Of course, if you are in the same php file, you can write the calling function before the function declaration.

Reason 6: You use the same name twice in a row to define a function, such as

function myFunction(){}

function myFunction(){}

The results are as follows

Fatal error:Cannot redeclare myfunction()(previously declared in(path):2)in(path) on line 1

Solution:

Find the already declared function and see what needs caused you to define it again. If you simply forgot that it was defined before, just delete one of the declarations. Of course, your situation may be complicated. For example, your script files are arranged in an extremely confusing manner, and you may use a large number of include() and other functions, which will make it difficult for you to sort out your ideas from the confusing code.

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