04-structs - CPE 357 - Systems Programming Fall 2009, Day 4...

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Unformatted text preview: CPE 357 - Systems Programming Fall 2009, Day 4 Structs and Memory Model Last Modified: Mon Sep 28 11:23:50 PDT 2009 Structs: Example: struct planet { char name[30]; double distance; // km int order; } mercury, venus; // optional structure tag. // optional variable names. struct planet mars, jupiter; struct planet earth = {"earth", 150e6, 3}; mars.order = 4; mars.distance = 230e6; strcpy(mars.name, "mars"); struct planet orb; orb = earth; struct planet *orbptr; orbptr = &orb; struct planet *pptr; orbptr = &venus; orb.order = 4; orbptr->distance = 108e6; strcpy(orbptr->name, "venus"); *pptr = *orbptr; can also pass either pointers or structures in and out of functions. arrays: struct planet balls[8]; balls[0].order = 1; balls[0].distance = 60e6; strcpy(balls[0].name, "mercury"); arrays of pointers struct planet *pballs[1000]; pballs[2] = &earth; pballs[7] = (struct planet *) malloc (sizeof(struct planet)); if (!pballs[7]) { perror("malloc failure"); exit(EXIT_FAILURE); } list of planets: struct pnode { struct pnode* next; struct planet data; } struct pnode * nptr = (struct pnode*) malloc(sizeof(struct pnode)); if (!nptr) { perror("malloc failure"); exit(EXIT_FAILURE); } Unions A union is used to hold different things at different times. It can hold only one thing at a time. The program needs to keep track of the right attitude / nature of the contents. The variable is large enough to hold the largest of the possibilities. The syntax is the same as for structs. Often a struct is used to wrap a union and disambiguate the contents. enum u_e {INT, DOUBLE, STR, CHAR} u_e; typedef union u_t {int i; double d; char *str; char ch} u_t; typedef struct s_t {u_e type; u_t data} s_t; Typedef: preferred typedef struct planet planet_t; typedef struct node { struct node *next; planet_t data; } node_t; Malloc/free remember not to leak memory. remember realloc and calloc Alignment mallocsize.c Use of MALLOC_CHECK (environment) Use of _FORTIFY_SOURCE BitFields if there's time (there wasn't when I did this in winter 2009) unsigned int a :3; signed int b: 5; they are not arrays. They do not have addresses. They are ints only. They are implementation-dependent in almost every way. LAB: Write a program that reads characters into a list, inserting at the head, then uses the list to print the string backwards. Define the list elements as structs. vim: set sts=2 sw=2 ai et : ...
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