问题
I just discovered something.
echo $var1 , " and " , $var2;
is the same as:
echo $var1 . " and " . $var2;
What is the actual string concatenation operator in php? Should I be using . or ,?
回答1:
The . operator is the concatenation operator. Your first example only works because the echo 'function' (technically it's a language construct, but lets not split hairs) accepts more than one parameter, and will print each one.
So your first example is calling echo with more than one parameter, and they are all being printed, vs. the second example where all the strings are being concatentated and that one big string is being printed.
回答2:
The actual concatenation is . (period). Using , (comma) there, you are passing multiple arguments to the echo function. (Actually, echo is not a function but a PHP language construct, which means you can omit the parentheses around the argument list that are required for actual function calls.)
回答3:
In the first case you just echo 3 different strings.
In the second case you concatenate the 3 strings and then echo the output.
So the answer is that, in order to concatenate strings you should use the dot (.)
回答4:
".". The other just writes several values independently, without actually concatenating the string.
See also PHP echo reference, the "," variant will only work with methods accepting multiple parameters.
回答5:
"." concatenates, "," can only be used for echo which is a language construct (sort of a function)
also see: Difference between period and comma?
回答6:
Using a comma doesn't actually concatenate the strings.
See this answer to another question.
回答7:
The "." is the correct concatenate operator. "echo" also accepts ",", treating it as if you are passing in a series of arguments to the "echo" method and then echoing each one. It's not truly concatenating the strings.
回答8:
nop it's because echo could take more then one argument, it would do the print each arguments
来源：https://stackoverflow.com/questions/1491198/php-string-concatenation-using