How to debug PHP code under Linux when just an blank page is shown?

I am newbie on PHP. Here is my situation: I write my code in vim and put it under /var/www/ then I visit this to run my code on browser:

http://localhost/***.php

When my code has a bug, it shows a blank page.

How can I debug my code 开发者_运维问答like C++ or Java?

Thanks.

Edited:

The link some friends provide is not helpful for me. I am under Linux. That's for Windows.

include this both line in code to see what kind of error is.

<?php 
       ini_set("display_errors",1);
       error_reporting(E_ALL);
        //code goes here
?>

For more advanced solution, you can use XDebug extension for PHP.

By default when XDebug is loaded, it should show you automatically the backtrace in case of any fatal error. Or you trace into file (xdebug.auto_trace) to have a very big backtrace of the whole request or do the profiling (xdebug.profiler_enable) or other settings. If the trace file is too big, you can use xdebug_start_trace() and xdebug_stop_trace() to dump the partial trace.

Installation

Using PECL:

pecl install xdebug

On Linux:

sudo apt-get install php5-xdebug

On Mac (with Homebrew):

brew tap josegonzalez/php
brew search xdebug
php53-xdebug

Example of mine configuration:

[xdebug]

; Extensions
extension=xdebug.so
; zend_extension="/YOUR_PATH/php/extensions/no-debug-non-zts-20090626/xdebug.so"
; zend_extension="/Applications/MAMP/bin/php/php5.3.20/lib/php/extensions/no-debug-non-zts-20090626/xdebug.so" ; MAMP

; Data
xdebug.show_exception_trace=1       ; bool: Show a stack trace whenever an exception is raised.
xdebug.collect_vars = 1             ; bool: Gather information about which variables are used in a certain scope.
xdebug.show_local_vars=1            ; int: Generate stack dumps in error situations.
xdebug.collect_assignments=1        ; bool: Controls whether Xdebug should add variable assignments to function traces.
xdebug.collect_params=4             ; int1-4: Collect the parameters passed to functions when a function call is recorded.
xdebug.collect_return=1             ; bool: Write the return value of function calls to the trace files.
xdebug.var_display_max_children=256 ; int: Amount of array children and object's properties are shown.
xdebug.var_display_max_data=1024    ; int: Max string length that is shown when variables are displayed.
xdebug.var_display_max_depth=3      ; int: How many nested levels of array/object elements are displayed.
xdebug.show_mem_delta=0             ; int: Show the difference in memory usage between function calls.

; Trace
xdebug.auto_trace=0                 ; bool: The tracing of function calls will be enabled just before the script is run.
xdebug.trace_output_dir="/var/log/xdebug" ; string: Directory where the tracing files will be written to.
xdebug.trace_output_name="%H%R-%s-%t"     ; string: Name of the file that is used to dump traces into.

; Profiler
xdebug.profiler_enable=0            ; bool: Profiler which creates files read by KCacheGrind.
xdebug.profiler_output_dir="/var/log/xdebug"  ; string: Directory where the profiler output will be written to.
xdebug.profiler_output_name="%H%R-%s-%t"      ; string: Name of the file that is used to dump traces into.
xdebug.profiler_append=0            ; bool: Files will not be overwritten when a new request would map to the same file.

; CLI
xdebug.cli_color=1                  ; bool: Color var_dumps and stack traces output when in CLI mode.

; Remote debugging
xdebug.remote_enable=off            ; bool: Try to contact a debug client which is listening on the host and port.
xdebug.remote_autostart=off         ; bool: Start a remote debugging session even GET/POST/COOKIE variable is not present.
xdebug.remote_handler=dbgp          ; select: php3/gdb/dbgp: The DBGp protocol is the only supported protocol.
xdebug.remote_host=localhost        ; string: Host/ip where the debug client is running.
xdebug.remote_port=9000             ; integer: The port to which Xdebug tries to connect on the remote host.
xdebug.remote_mode=req              ; select(req,jit): Selects when a debug connection is initiated.
xdebug.idekey="xdebug-cli"          ; string: IDE Key Xdebug which should pass on to the DBGp debugger handler.
xdebug.remote_log="/var/log/xdebug.log" ; string: Filename to a file to which all remote debugger communications are logged.

If on a localhost, I would suggest using firefox or chrome and installing firebug for mozilla, and chrome gets a default. Be sure that on a local host your settings are matched to the server you are uploading to as this can cause problems when going live.

Specifically most shared hosting has PHP on safe mode and output buffering off, so if you use it, use it by calling it by calling ob_start(); etc, otherwise you should have no problems, and learning to debug is part of the fun, helps you learn alot :)

As for php errors just re-edit your php.ini file, you can find al relevant information on http://php.net

Happy Coding

You can use error_reporting() at the top of your code...

error_reporting(E_ALL);

You will also want display_errors on in php.ini.

Note that you should have public facing error reporting off in a production environment.

Though i personally find var_dump just enough for my php debugging, some people tend to like using debuggers like xdebug to do so.

PHP produces an error_log file in its directory whenever a problem occurs, you can find debug information there.

Also, try using var_dump($someVarible). This will give you useful information about the current state of a variable - often better than echo.

In addition to the comments about using error_reporting(E_ALL); at the top of your code, I like to use the php cli utility. I don't have a web server on the pc that I use to write and debug php and html, so a nice feature of the cli utility is the built-in web server. To install the php cli:

sudo apt install php7.0-cli

To use the web server, cd to the directory where your html and php files are located and run:

php -S localhost:8080

Then point your browser to the files you're testing...for example:

http://localhost:8080/test.php 

You can also use the cli utility to run your php code, and it will display the errors by line number (use an editor that displays line numbers). You may need to comment out and adjust code that depends on html calling it.

php test.php

Use these two lines to debug (this will enable to find the errors on the line numbers):

ini_set('display_errors', 'On');
error_reporting(E_ALL | E_STRICT);

You can check the log file output by PHP. A good way to see your configuration is to use phpinfo().

Also you can set error_reporting() so you can see the error message instead of a white page.

In most cases, if you set you error_reportto -1 you'll be able to see all notices, warning and errors in your browser.

There are many options:

• use the error_reporting() function to have your code report even the slightest warning. Alternatively look in the server's error log file.
• use var_dump(), print_r() and echo to look at your variables.
• use debug_backtrace() and debug_print_backtrace() to see your call stack.
• use xdebug. Xdebug provides debugging by using breakpoints and stepping through the code, tracing and profiling. Xdebug is a PHP extension. You can run it standalone by giving commands on the command line, an environment variable or an ini file.
• More user friendly is to use a program to interface with Xdebug. This interface goes by default via port 9003 (9000 in older Xdebug versions). Popular programs for this purpose are PHPStorm, Netbeans and Visual Studio.

Note that Xdebug seriously slows down your server. So switch it off when you don't use it.