The error_reporting() function sets the error_reporting directive at runtime. PHP has many levels of errors, using this function sets that level for the duration (runtime) of your script.
The new error_reporting level. It takes on either a bitmask, or named constants. Using named constants is strongly encouraged to ensure compatibility for future versions. As error levels are added, the range of integers increases, so older integer-based error levels will not always behave as expected.
The available error level constants are listed below. The actual meanings of these error levels are described in the predefined constants.
Returns the old error_reporting level.
Example 1. error_reporting() examples
With PHP > 5.0.0 E_STRICT with value 2048 is available. E_ALL does NOT include error level E_STRICT (but in PHP 6 it does though). Most of E_STRICT errors are evaluated at the compile time thus such errors are not reported in the file where error_reporting is enhanced to include E_STRICT errors.