echo () function outputs one or more strings
print () function outputs one or more strings.
Note: echo () function of the ratio () Print speed slightly faster. print_r function can only output value of a variable, echo values of a plurality of output variables can be
unset () function is used to destroy the given variable.
Note: The definition of a variable, if the variable is not required once, you can use the unset () function is destroyed, freeing memory.
isset () function
syntax: boolean empty (mixed var)
Function: determining whether the variable exists. Returns true existence, false otherwise
- isset () function for detecting whether a variable is set and a non-NULL.
- If, after use has been unset () released a variable, then through isset () determines the return FALSE.
- When using isset () test is a variable set to NULL and returns FALSE.
- Also note that the null character ( "\ 0") is not equivalent to the PHP NULL constant.
empty () function
syntax: boolean empty (mixed var)
Function: to check the variable var is "empty", the function var parameter variable name ($ band number). If the variable var is empty, empty () function returns TRUE, otherwise it returns FALSE.
Note: Use empty () function, the variable is "empty" meaning: If the variable var is "", 0, "0" , 0.0, NULL, FALSE , or array (), will be considered null. empty () function only for detecting whether a variable is "empty", other transmission parameters will cause the program to resolve the error.
- empty () function is used to check whether a variable is null.
- empty () to determine whether a variable is considered empty. When a variable does not exist, or it is equivalent to the value FALSE, the absence of it will be considered. If the variable does not exist, empty () does not generate a warning.
DEFINE () function defines a constant.
Similarly constant variable, except that:
- After setting the constant value can not be changed
- Constant names do not begin with a dollar sign ($)
- Scope does not affect access to the constants
- Constant value can only be strings and numbers
constant () function returns a constant value.
