Is 0 necessary in 0777 here in PHP?

mk开发者_开发知识库dir("/path/to/my/dir", 0700);

Is the 0 in 0777 necessary?

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Yes. The leading zero will make the number interpreted as octal number; without it would be interpreted as decimal number.

var_dump(0700); // int(448)
var_dump(700);  // int(700)

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The leading zero indicates an octal value. See also the documentation of chmod.

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Yes. It's an octal literal