The difference between strlen and sizeof

Catalog

1. What is? sizeof

2. What is? strlen

strlen and sizeof The difference between ：

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1. What is? sizeof

sizeof It's a Operator , Its value has been calculated during compilation , Its parameters can be arrays 、 type 、 object 、 Functions, etc .

function ： Calculate the maximum bytes of space occupied by this parameter

Because computation occurs during compilation , therefore sizeof Only non dynamic objects can be calculated ,sizeof The return value of is independent of the content of the passed in parameter , And its return value is size_t type , That is to say unsigned int type .

2. What is? strlen

strlen It's a function , Its value is calculated at runtime ,strlen The parameter of must be char* type

function ： Calculate encounter '\0' Number of all previous characters

strlen and sizeof The difference between ：

1. sizeof It's the operator You don't need to add parentheses , and strlen Is the function Parentheses must be added
2. sizeof You can take the type as the parameter , and strlen Can only be char* As a parameter
3. Array as sizeof Parameters of are not degraded , And as a strlen Will degenerate into char* The pointer
4. strlen The size of is calculated at runtime , and sizeof The size of is calculated at compile time
5. sizeof It calculates the space occupied by the whole parameter , and strlen The calculation is to meet '\0' Number of all previous characters