12.6 Arrays of Structures

I l @ ve RuBoard

Structures and arrays can be combined. Suppose you want to record the time a runner completes each lap of a four-lap race. You define a structure to store the time:

 struct time {      int hour;   // Hour (24-hour clock)     int minute; // 0-59     int second; // 0-59 };  const int MAX_LAPS = 4; /* We will have only 4 laps*/  /* The time of day for each lap*/  struct time lap[MAX_LAPS]; 

The statement:

 struct time lap[MAX_LAPS]; 

defines lap as an array of four elements. Each element consists of a single time structure.

You can use this as follows :

 /*   * Runner just past the timing point   */  assert((count >= 0) && (count <= sizeof(lap)/sizeof(lap[0]))); lap[count].hour = hour;  lap[count].minute = minute;  lap[count].second = second;  ++count; 

This array can also be initialized when the variable is declared. Initialization of an array of structures is similar to the initialization of multidimensional arrays:

 struct time start_stop[2] = {      {10, 0, 0},      {12, 0, 0}  }; 

Suppose you want to write a program to handle a mailing list. Mailing labels are 5 lines high and 60 characters wide. You need a structure to store names and addresses. The mailing list will be sorted by name for most printouts, and in Zip-code order for actual mailings . The mailing list structure looks like this:

 struct mailing {      char name[60];    // Last name, first name     char address1[60];// Two lines of street address     char address2[60];      char city[40];    // Name of the city      char state[2];    // Two-character abbreviation  [2]  long int zip;     // Numeric zip code }; 

^[2] To store the state abbreviation as a C-style string, three characters are needed; two for the data and one for the end-of-string character. This is not a C-style string. Instead it is just two characters. So the dimension 2 is correct.

You can now declare an array to hold the mailing list:

 /* Our mailing list */  struct mailing list[MAX_ENTRIES]; 

I l @ ve RuBoard