Comparison between strlen and sizeof

1. strlen () is used to calculate the length of the specified string S, excluding the ending character '\ 0 '. Strlen only works as a counter. It starts scanning from a memory location (which can start with a string, a location in the middle, or even an uncertain memory area, Until the first string Terminator '\ 0' is met, Then return the counter value, inProgramRuntime computing.

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2. sizeof is an operator that can be used for any variable name, type name, or constant value. It does not need parentheses when used for variable names (not array names) or constants.

It works during compilation rather than runtime.

Sizeof () is returned after the variable Declaration Actual memory bytes occupied , Not the length. In addition, sizeof is not a function, but an operator. strlen is a function.

3. example

char CHS [] = {'A ', 'C', '/0', 'z', '3', 'D'}; // sizeof (CHS) = 6; and strlen (CHS) = 2.

http://www.cnblogs.com/ffhajbq/archive/2012/11/14/2769211.html

char STR [20] =" 0123456789 ";

int A = strlen (STR ); // A = 10;

int B = sizeof (STR ); // B = 20;

4. sizeof can be used as a parameter, strlen can only use char * as a parameter, and must end with ''\ 0. If sizeof is a type, you must add an arc. If it is a variable name, you can do not add an arc. This is because sizeof is an operator and not a function. The sizeof operator cannot return the size of the dynamically assigned array or external array.

the sizeof parameters of arrays are not degraded, passing to strlen degrades to a pointer (because strlen is a function ).

5. when sizeof is used, a special case is that the array name changes to pointer,

char array [3] = {'0 '};

sizeof (array) = 3;

char * P = array;

strlen (p) = 1; // The sizeof (p) result is 4

when passing an array name to a function, it will be completely degraded into a pointer.

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