复旦大学软件学院计算机系统课件 Array.pptVIP

* * * * * * Command-line Arguments $ echo hello, world $ hello, world #include stdio.h /* echo command-line arguments */ main(int argc, char *argv[]) { int i ; for ( i = 1; i argc ; i++) printf(“%s%s”, argv[i], (i argc-1) ? “ ” : “”); printf(“\n”) ; return 0; } 0 echo\0 Hello,\0 World\0 argv: Command-line Arguments #include stdio.h /* echo command-line arguments ; 2nd version*/ main(int argc, char *argv[]) { while ( --argc 0 ) printf(“%s%s”, ++argv, (argc 1) ? “ ” : “”); printf(“\n”) ; return 0; } printf((argc 1) ? “%s ” : “%s”); Pointer to Function #include stdlib.h /* numcmp: compare s1 and s2 numerically */ int numcmp(char *s1, char *s2) { double v1, v2; v1 = atof(s1); v2 = atof(s2); if (v1 v2) return -1; else if ( v1 v2 ) return 1; else return 0; } Pointer to Function #include stdio.h #include string.h { …… int numeric = 0, (*cmp)(void *, void *); char *s1, *s2; …… if (…) numeric = 1 ; …… cmp = ( int (*)(void *, void *)) (numeric ? numcmp : strcmp); (*cmp)(s1, s2); …… } * * * * * * * * * * * * * * * * * * * * * * * * * * * * Compilers Autumn 2002 Compilers Autumn 2002 * Array * Outline Aggregate scalar data into larger data Pointers vs. Array Array subscript and pointer arithmetic Memory layout for array Static vs. dynamic Compiler optimization for array operations Suggested reading 3.8 * Array declaration T A[N] ; Allocate a contiguous region in memory The size of the region is sizeof(T) * N bytes * Starting Address of an Array The starting address of an array A is denoted as XA Identifier A can be used as A pointer to the beginning of the array Its value is XA * Accessing Array Array elements can be accessed Using an integer index ranging between 0 and N-1 Array element i is stored at address XA + sizeof(T) * i * Array 0 1 2 3 4 5 6 7 8 9 10 11 0 4 8 12 16 char a[12] ; xa xa+4 xa+8 char *b[5] ; xb xb+4 xb+8 xb+12 xb+16 * Array 0 4 8 12 16 double c[2] ; xc xc+8 double *d[5] ; xd xd+4 xd+8 xd+12 xd+16 * Pointe