北京大学计算概论课件第十四讲 指针.pptVIP

Linux+ Guide to Linux Certification, Second Edition A First Book of ANSI C, Fourth Edition Lesson 14Pointer arithmetic 2007/11/14 Objectives Array and Pointer arithmetic Pointer to array and multidimensional array Processing Strings Using Pointers Creating Strings Using Pointers Common Programming and Compiler Errors Subscript to address (offset) Types of Pointers int *ptr ; char *ptr; void *ptr; Pointers with subscript Pointer as array name Subscript variable VS Dereferencing Pointer arithmetic Pointer arithmetic (cont.) Manipulating Pointers A pointer, constructed either as a variable or function parameter, contains a value: an address By adding numbers to and subtracting numbers from pointers, we can MOVE pointer to different elements The addresses in pointers can be compared using any of the relational operators (==, !=, , , etc.) Pointers can be initialized when they are declared Exp: copy string Pointer to arrays #define ROWS 2 #define COLS 3 int nums[ROWS][COLS] = { {16,18,20}, {25,26,27} }; Pointer to arrays (cont.) Pointer to arrays (exp.) Pointer to arrays (exp.2) Pointer to arrays (exp.3) Pointer to arrays (cont.) A function that receives an integer two-dimensional array can be declared as: calc(int pt[2][3]) calc(int pt[][3]) calc(int (*pt)[3]) It refers to a single pointer of objects of three integers The following declaration would be wrong: calc(int *pt[3]) It refers to an array of three pointers, each one pointing to a single integer Creating Strings Using Pointers The definition of a string automatically involves a pointer (a pointer constant) Strings cannot be copied using an assignment operator The strcpy is invalid here char *message; strcpy(message, abcdef ); Array of pointer Example: char *seasons[4]; seasons[0] = Winter; seasons[1] = Spring; seasons[2] = Summer; seasons[3] = Fall; Or: char *seasons[4] = {Winter,Spring, Summer, Fall}; Pointer Arrays (continued) Pointer Arrays (con