Variable-length array in C Language

Source: Internet
Author: User
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. Int main (INT argc, char * argv [])
  6. {
  7. Int I, N;

  8. N = atoi (argv [1]);
  9. Char arr [n + 1];
  10. Bzero (ARR, (n + 1) * sizeof (char ));

  11. For (I = 0; I <n; I ++ ){
  12. Arr [I] = (char) ('A' + I );
  13. }
  14. Arr [N] = '/0 ';
  15. Printf ("% s/n", arr );

  16. Getchar ();
  17. Return (0 );

  18. }

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


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