Array size macro: #define ARRAY_SIZE(x) (sizeof(x) / sizeof((x)[0])) // Used like this: int a[] = {0, 5, 6}; int n = ARRAY_SIZE(a); // n = 3 // Warning: does not work with array arguments to // functions: int func(int a[]) { int nb = ARRAY_SIZE(a); // Doesn't work! }
Hello World: #include <stdio.h> int main(void) { printf("Hello, World!"); return 0; }
malloc(0) can return either a null pointer or a pointer to 0 bytes. The ANSI/ISO Standard says that it may do either and that the behaviour is implementation-defined.
Difference between ++i and i++: ++i adds one to the stored value of i and ``returns'' the new, incremented value to the surrounding expression; i++ adds one to i but returns the prior, unincremented value.
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Count the number of bits which are set in an integer: static int bitcounts[] = {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 += bitcounts[u & 0x0f]; return n; }
difference between memcpy and memmove: memmove offers guaranteed behavior if the memory regions pointed to by the source and destination arguments overlap. memcpy makes no such guarantee, and may therefore be more efficiently implementable.
The postfix ++ and -- operators have higher precedence than the prefix unary operators. Therefore, *p++ is equivalent to *(p++); it increments p, and returns the value which p pointed to before p was incremented. To increment the value pointed to by p, use (*p)++
Array subscripting is commutative in C. a[e] is identical to *((a)+(e)), for any two expressions a and e, as long as one of them is a pointer expression and one is integral. For example: char *tmpptr = "abcdef"; now tmpptr[5] is 'f' and 5[tmpptr] is also 'f'.
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