Variable-length array in C Language

Variable-length array in C Language

We know that the traditional C language does not support variable-length arrays as C ++ does. That is to say, the length of arrays is determined during compilation and cannot be changed during runtime. The new features of C language are defined in the c99 standard. A new feature allows you to use variable-length arrays in C.

C99 gives C programmers the ability to use variable length arrays, which are arrays whose sizes are not known until run time. A Variable Length array declaration is like a fixed array declaration limit t that the array size is specified by a non-constant expression. when the Declaration is encountered, the size expression is evaluated and the array is created with the indicated length, which must be a positive integer. once created, variable length array cannot change in length. elements in the array can be accessed up to the allocated length; accessing elements beyond that length results in undefined behavior. there is no check required for such out-of-range accesses. the array is destroyed when the block containing the Declaration completes. each time the block is started, a new array is allocated.

The above is the c99 standard description of the C language variable-length array.

C Variable Length array, the source code used for testing is very simple, as shown below:

1. // File name: dynarray. c
2. // Compilation environment: bloodshed Dev-C/C ++ 4.9
3. # Include <stdio. h>
4. # Define bzero (B, Len) (memset (B), '/0', (LEN), (void) 0)
5. 
   
7. Int main (INT argc, char * argv [])
8. {
10. Int I, N;
11. 
    
12. N = atoi (argv [1]);
14. Char arr [n + 1];
16. Bzero (ARR, (n + 1) * sizeof (char ));
17. 
    
19. For (I = 0; I <n; I ++ ){
21. Arr [I] = (char) ('A' + I );
23. }
25. Arr [N] = '/0 ';
27. Printf ("% s/n", arr );
28. 
    
30. Getchar ();
31. Return (0 );
32. 
    
34. }

The above program is named dynarray. C. The job is to add 1 to the value n of argv [1] As the length of ARR, And the ARR type of the variable-length array is Char. Then write some characters into the array and output the written strings.

After compiling on the c 99 standard IDE, run:

C:/c99_test/dynarray.exe 6

Output:

Abcdef