How to debug PHP functions?

In order to debug PHP functions, there are several practical techniques: use var_dump() to output the type and value of the variable. Use print_r() to output variables in a readable string format. Use echo to output text. Use Xdebug's advanced debugging features, such as setting breakpoints for deeper troubleshooting.

How to debug PHP functions

Debugging PHP functions is critical to identifying and solving program problems. This article will provide practical tips for different situations.

Method 1: Use var_dump()

This function outputs the type and value of the variable. Add it to the function code like:

function sum($a, $b) {
  var_dump($a);
  var_dump($b);
  return $a + $b;
}

After calling the function, you can see the value of the input variable.

Method 2: Use print_r()

This is similar to var_dump(), but formatted into a readable string:

echo print_r($variable, true);

Method 3: Use the echo

echo statement to simply output text:

function sum($a, $b) {
  echo "a is $a<br>";
  echo "b is $b<br>";
  return $a + $b;
}

Method 4: Use Xdebug

This is an advanced debugger that provides more features. Install Xdebug and configure PHP:

;php.ini
zend_extension=xdebug.so

Then use xdebug_break() to set breakpoints at specific points in the code.

Practical case: debugging summation function

Let’s use these methods to debug a summation function:

function sum($a, $b) {
  if ($a < 0 || $b < 0) {
    throw new Exception('输入值不能为负数');
  }
  return $a + $b;
}

• Method 1 (var_dump()): Given the inputs -1 and 2, var_dump() displays -1 is a mismatched input type, thus identifying an error.
• Method 2 (print_r()): Display a clearer human-readable error message.
• Method 3 (echo): Output a specific error message, such as "The input value cannot be a negative number".
• Method 4 (Xdebug): Set a breakpoint to stop execution when an exception is thrown.

Conclusion

By using these debugging techniques, you can easily troubleshoot and resolve problems in your PHP functions. Choose the most appropriate tool for the situation and carefully review the output to identify errors.

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