for($i=1;$i<=3;++$i){ require 'command1.php'; }
原本想要包含并执行这个echo，没想到写错了文件名，如果是require，会报出这样的错误：
Warning: require(command1.php): failed to open stream: No such file or directory in console.php on line 4 Fatal error: require(): Failed opening required 'command1.php' (include_path='.') in console.php on line 4 PHP Warning: require(command1.php): failed to open stream: No such file or directory in console.php on line 4 PHP Fatal error: require(): Failed opening required 'command1.php' (include_path='.') in console.php on line 4
如果把require改为include
for($i=1;$i<=3;++$i){ include 'command1.php'; }
会报出这样的错误：
Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4 Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4 Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4 Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4 Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4 Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4 PHP Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4 PHP Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4 PHP Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4 PHP Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4 PHP Warning: include(command1.php): failed to open stream: No such file or directory in console.php on line 4 PHP Warning: include(): Failed opening 'command1.php' for inclusion (include_path='.') in console.php on line 4
如果使用require_once或者include_once，只要包含路径正确，那么循环只执行一次。
总结：
使用require，如果文件没有包含成功，就会报出一个fatal error，整个程序就中止了。
使用include，如果文件没有包含成功，就会报出一个普通的warning，之后的代码仍会执行。
如果你的Web程序使用了MVC这种对文件包含强依赖的设计方法，请使用require_once。
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