Lecture 6 - More Structures, Declaration vs. Definition, String Functions

Question 1

what does this do?
gcc -o hw1 hw1_test.o

Answer 1

• links the object file hw1_test.o and produces an executable file named hw1
• if you have compiled hw1_test.o correctly you will now be able to use ./hw1

Question 2

how about a struct typedef

Answer 2

• works same as before
• pretend you’re defining a struct
• ex. struct my_data md;
  variable and change it to a typedef
• ex. typedef struct my_data md;

Question 3

often we declare the typedef when we declare the struct…

Answer 3

typedef struct my_new_struct {
int x;
float y;
} new_struct_type;
- typedef keyword goes before struct declaration
- name used for type_def is BEFORE the semicolon

Question 4

definition

Answer 4

• allocates storage for a variable (or function)
• ex. int x = 10;
• ALL definitions are also declarations

Question 5

declaration

Answer 5

• announces the properties of a variable (or function)
• ex. int x;

Question 6

definition vs. declaration

Answer 6

definition allocates memory AND announces the properties of a variable, declaration just announces the properties

Question 7

function prototype

Answer 7

• a forward declaration declaration
• double some_function(int, float);
• the creation of that function is a definition

Question 8

where to put declarations/definitions

Answer 8

• put pure declarations OUTSIDE of functions
• put definitions (e.g. variables) inside functions

Question 9

structures inside structures

Answer 9

• you can define structured variables inside other structures

struct segment {
struct coord one;
struct coord two;
};
- when you initialize, you need extra braces
- struct segment my_seg = { {0, 0, 0}, {0, 0, 0} };

Question 10

arrays in structures

Answer 10

• you can define array variables in structure declarations
  struct person {
  char name[40];
  char title[15];
  int codes[4];
  };
• definition/initialization
• ex. struct person jt = {“Jeff Turkstra”, “Troublemaker”, {10, 20, 25, 9} };

Question 11

assignment of elements in an array from a structure

Answer 11

• ex. struct person jr = {“”, “” {0, 0, 0, 0] };
• ex. jr.codes[0] = 5;
• ex. jr.codes[1] = 10;

Question 12

compound literals

Answer 12

• can cast a list to a struct
• ex. jr = (struct person) {“Who”, “what”, {1, 2, 3, 4} };

Question 13

what #include to use functions that manipulate strings

Answer 13

include <string.h></string.h>

Question 14

global variables

Answer 14

• global variable definition is one that exists outside of any function (AVOID when possible)

Question 14

strncpy

Answer 14

• strncpy(char *dest, const char *src, size_t n);
• dest is buffer where string is copied, src is source string to copy from, n is max number of character to copy
• ex. strncpy(jr.name, “jon”, 3);

Question 15

string comparison functions

Answer 15

• strcmp(first string, second string)
• returns 0 if they are equal, negative number is str1 after str2 lexicographically, and pos for opposite

Question 16

determine the length of a string

Answer 16

• strlen()
• ex. char name[20] = “Jeff”;
• strlen(name)

Question 17

is a typedef a declaration or definition

Answer 17

• it turns a variable definition into a type declaration