C Language Small Program

Recently in reading C language book, feel also quite interesting, a bit of harvest, collected a few beautiful small procedures, with the grand total reward!

1) Replace the 10 binary number with the small function of any binary number

Char *baseconv (unsigned int num, int base) {    static char retbuf[33];    char *p;    if (Base < 2 | | Base >)        return NULL;    p = &retbuf[sizeof (RETBUF)-1];    *p = ' + ';    do{        *--p = "0123456789abcdef" [num% base];        Num/= base;    } while (num! = 0);    return p;}

"ABCdef" [5] can be understood as

Char *p = "abcdef"; ... p[5] ...

Arrays and subscripts are interchangeable in the C language, so they can also be written as 5["abcdef" (not advocating ha, for reasons you know)

2) calculates the number of bits in an unsigned integer as 1

static int bittab[] = {    0,1,1,2,    1,2,2,3,    1,2,2,3,    2,3,3,4};int bitcount (unsigned int u) {    int n = 0; for       (; U! = 0; u >>= 4)        n + = bittab[u & 0x0f];    return n;}

There's nothing to introduce about the bitwise operation, so let's think about the structure of Bittab.

3) Encapsulation of the free function

void Saferfree (void **pp) {    if (pp! = null && *PP! = null) {free        (*PP);        *PP = NULL;}    } #define SAFEFREE (P) saferfree ((void**) & (P))

The free function does not check if the incoming pointer is null, nor does it set the pointer to null before returning. It's a good habit to set it to null after releasing the pointer.

C Language Small Program