A summary of the sizeof function in C language

The result of the sizeof function:

2. Variable: The number of bytes that the variable occupies.

   int 0 ;p rintf ("%d\n"sizeof(i));    // 4

3. Array: The number of bytes that the array occupies.

   intArr_int1[] = {1,2,3,4,5};intarr_int2[Ten] = {1,2,3,4,5};p rintf ("size_arr1=%d\n",sizeof(Arr_int1));//5*4=20printf"size_arr2=%d\n",sizeof(Arr_int2));//10*4=40

5. String: Actually, it is an array of characters that have been added ' \ s '. The result is a string character length of +1.

   Char " Str " ;p rintf ("size_str=%d\n",sizeof(str));    // 3+1=4

6. Pointer: fixed Length: 4 (32-bit address environment).
   • Special Description: When an array is an entry parameter to a function, the logarithm of the group sizeof in the function is fixed to 4: Because the passed-in parameter is a pointer.

      int  get_size (int   arr[]) { return  sizeof  Span style= "COLOR: #000000" (arr);}  int   main () { int  arr_int[10 ] = {1 , 2 , 3 , 4 , 5  }; printf (  " size_fun_arr=%d\n   ", Get_size (Arr_int)); // 4 } 

7. Structural body
   1. Structure with variables only:
      2. The result is an integer multiple of the maximum number of bytes for the widest variable: [4 1 xx x]

         struct Test {    int  i;     Char ch;} test_t;printf ("size_test=%d\n"sizeof(test_t));    // 8

      4. several variables with a smaller width can be populated within a width range: [4 2 1 1]

          typedef struct   Test { int   I    ;     short   S;     char   ch1;  char   CH2;} test_t;printf (  " size_test=%d\n     Span style= "COLOR: #800000" > ", sizeof  (test_t)); // 8  

      6. address alignment: The offset of a struct member must be an integer multiple of its own width: [4 1 x 2 1 x x x]

          typedef struct   Test { int
                    I;     char   ch1;     short   S;  char   CH2;} test_t;printf (  " size_test=%d\n     Span style= "COLOR: #800000" > ", sizeof  (test_t)); // 12  

   3. struct with array: Contains the width of the entire array. The array width is detailed above. [4*10 2 1 1]

      struct Test {    int i[];      Short s;     Char ch1;     Char CH2;} test_t;printf ("size_test=%d\n"sizeof(test_t));    //  -

   4. Structure of nested structure body
      2. Contains the width of the entire internal structure (that is, the entire expanded internal structure): [4 4 4]

         struct son {    int  name;     int birthday;    } son_t;     struct Father {    son_t  s1;     int Wife;} father_t;printf ("size_struct=%d\n",sizeof(father_t));    //  A

      3. Address alignment: The internal structure of the expandedoffset for first member, it must be unfolded.the widest variable in the internal structureInteger multiples of the occupied bytes: [2x x2 x x 4 4 4]

         struct Son {    short age  ;     int name;     int birthday;    } son_t;     struct Father {    short age  ;    son_t  S1;     int Wife;} father_t;printf ("size_struct=%d\n",sizeof(father_t));    //  -

A summary of the sizeof function in C language