Breakpoints

Breakpoints are essential tool for debugging your applications. You set the breakpoints whenever you want to pause the execution. When paused you can investigate the program's state - check the values of variables or look at the call stack.

Set breakpoint on line in source code

You can set the breakpoint on any line of executable code by clicking in the margin of the code editor, or by right-clicking on a line of code and selecting Breakpoint, Insert Breakpoint, or simply by pressing F9 (This is a typical shortcut; check the Debug, Toggle breakpoint in the settings menu).

Breakpoint

When you debug, the debugger will pause the execution before the line with the breakpoint is executed.

Executable code and breakpoint resolution

The breakpoint will only work when placed on a location associated with actual PHP executable code.

When breakpoint is placed on the location without PHP executable code, breakpoint resolution mechanism is used to move the breakpoints to line where they can break (it has to be within 5 lines). This feature is supported since Xdebug version 2.8 and higher.

Breakpoint conditions

You can control when breakpoint stops the execution of the program by setting conditions.

To set a breakpoint condition:

  • right click on the breakpoint symbol (in the editor left margin or in the Breakpoint window) and select Condition... (or press Alt + F9, C), which will open Breakpoint Settings window.

Breakpoint context menu

  • To set breakpoint condition, in the first drop down menu select Conditional Expression.

  • In the second drop down menu, choose Is true to break when the expression is satisfied, or When changed to break when the value of the expression has changed.

    Conditional Breakpoint dialog

    Note: When the breakpoint with When changed condition is first evaluated, the debugger doesn't consider it to be a change, so it doesn't break.

Set hit count condition

When you want a breakpoint to break after it has been hit certain amount of times, you can choose Hit Count in the Breakpoint Settings and specify number of iterations.

Tracepoint

This is feature is useful when you are noticing certain loop to misbehave after certain number of iterations. Rather than stepping through the loop by repeatedly pressing F5, use Hit count.

Tracepoints (Breakpoint Actions)

Tracepoint is a breakpoint that prints a message to Output pane - Debug when hit, but it doesn't break the execution of the program.

To set a tracepoint:

In Breakpoint Settings window check Actions and provide a log message. The log message can contain variables (placed between { and }), including predefined special variables listed bellow:

Keyword What is Displayed
$ADDRESS Current instruction
$CALLER Calling function name
$FUNCTION Current function name
$PID Process ID
$PNAME Process name
$TID Thread ID
$TNAME Thread name
$TICK Tick count (from Windows GetTickCount)

Tracepoint

Sample of the output is depicted bellow:

Tracepoint message in Output Pane

You can find the sample use-case here

Function breakpoints

You can break execution when a function is called. This is useful when you know function or method name, but you don't know the location (or you do know and you just don't want search for it). The other use case would be if there are multiple methods or function with the same name (e.g. same function in different namespaces or method implemeneted on multiple classes) and you would like to break on all of them.

  • To place a function breakpoint, go to Debug | New Breakpoint | Function Breakpoint, or press Ctrl + K, followed by B. Or if you have Breakpoints pane opened, click New and select Function Breakpoint

  • When in the New Function Breakpoint dialog, enter the function or method name.

    New Function Breakpoint dialog

  • Make sure PHP is select in the language drop down

  • Hit ENTER

If the function or method is in the project the breakpoint will bind.

When providing function name, you can be more specific. The syntax for the function breakpoint is <directory_string>!<type_name>::<function_name>(), where type_name and function_name can be fully qualified or the namespace part can be omitted.

These syntaxes are possible:

  • function_or_method_name
  • function_or_method_name()
  • fully\qualified\function_name
  • ::method_name
  • type_name::method_name
  • fully\qualified\type_name::method_name
  • directory_string!function_or_method_name
  • directory_string!type_name::method_name

Names that are not fully qualified will be searched for within available namespaces, so you can type the name without the namespace.

Tip: Restrict the breakpoints only to functions defined in files that have the specified directory_string! as a part of their path.

Break on Exception

You can define types of exception that should break your program when they are thrown. See Exceptions to find out more about this.

Managing breakpoints

To see all the breakpoints in your solution, open Breakpoints window from Debug | Windows | Breakpoints or press Ctrl+ Alt + B.

From this window you can enable/disable or delete breakpoints, search and sort them. You can change breakpoint settings directly from this dialog.

Breakpoints pane

Tip: You can see how many times the breakpoint was hit in the Hit Count column.