For my cs project I need to use a 2d table of strings, which will symulate database table. I don't know how to create such thing. Table should have 5 columns and number of rows should be increasing when new records are added. The max size of strings inside is 52 signs.
2 Answers
You have to create a dynamic 3d array to hold row, column and the char array.
To do this initiate the 3d-array with pointers
char ***table;
Each time you then add a new row to your "database" you have to expand the memory allocated to your table. I would suggest to initiate another variable which holds the current size of your table. To expand the memory you need by adding a new row you have to assign the amount of memory for current rows * (size-pointer) + size pointer. Then you have to allocate memory to this new pointer (size-pointer) * 5 for your columns. Then for each column assign the size of memory needed to the pointer of each column by either just allocating the max of 52 * (size-char) or even only the size of the string you want to save at the respective position. Use malloc() for adding a new value to your table and realloc() to change the size of existing levels, f.e. when adding a new row, because you then change the amount of memory allocated to your row-level.
This answer assumes you're familiar with dynamic arrays and memory allocation, as well as accessing them. Please leave a comment if you need further explanation or code examples as the above only discusses an idea how to deal with the problem.
Some examples:
//adding a new row
table = realloc(table, sizeof(char*)*(current_size+1));
table[current_size+1] = malloc(sizeof(char*)*5);
//now for every column do the following where i is the number for the current column
table[current_size+1][i] = malloc(52*sizeof(char));
You can then access the new created fields like so (i and k are for respective row and column):
table[i][k] = "Hello World";
Hope it helps!
4 Comments
user3426015
I will try to do that, but a bit of realloc and malloc code would be helpfull. Also thanks for help.
hallole
I added an example on how to adjust and manage memory for a new row; the code is untested though, but in principle it should work.
user3426015
int i=0; database = realloc(database, sizeof(char*)*(current_size+1)); database[current_size+1] = malloc(sizeof(char*)*5); while(i<5) { database[current_size+1][i] = malloc(52*sizeof(char)); ++i; } is it ok?
hallole
Should work I assume
You're probably going to need to define a data structure to use with your db, in case you need to search on the data. Something as simple as a list may suffice, depending on the complexity of your assignment. Here is a VERY simple example:
#include <stdio.h>
#include <stdlib.h>
typedef struct db
{
char col1[52];
char col2[52];
char col3[52];
char col4[52];
char col5[52];
struct db *next;
} DB_type;
DB_type* add_reg(DB_type* db_ptr);
int main(void)
{
DB_type *db_ptr = NULL;
db_ptr = add_reg(db_ptr);
db_ptr = add_reg(db_ptr);
db_ptr = add_reg(db_ptr);
DB_type *aux = db_ptr;
while (aux)
{
printf("%s %s %s %s %s\n", aux->col1, aux->col2, aux->col3, aux->col4,
aux->col5);
aux = aux->next;
}
return 0;
}
DB_type* add_reg(DB_type* db_ptr)
{
DB_type *new_data = (DB_type*) malloc(sizeof(DB_type));
printf("Add new data:\n");
scanf("%s %s %s %s %s", new_data->col1, new_data->col2, new_data->col3,
new_data->col4, new_data->col5);
printf("Done.\n");
if (db_ptr)
new_data->next = db_ptr;
else
new_data->next = NULL;
return new_data;
}
chararrays.new.