Inserting many records - c

Question

The output of the program generates random results for a 100 rounds of 100 coin tosses. I need to get all of those H & T results (10,000) into SQLite for analysis.
Round 1:
TTTTTHHTHTTHHTTTHHTTTTTTTHHTTHHHHHHTTTHTHTTHHTTTHHHHHHTHTTTTHTHHTHTTTHTHTHTHTTHHTTTTTTHTHTTHHTTTTHTH
-
Round 99:
TTHHHTHTHHTTTHHTTHTHTHTTHHHHHTHTTTTHHHHTHTHTHTHHHHTTTTTHTTHHHTTTTHTTHHHHTTTTTTHHTHTTHTTTTHTHHTTHHTHT
Round 100:
THTHTHHHHHTTHTTTTTTTTTTTHTTHHTHHHTHHTHHHHTTHTHHTTHTHTHHTTHHHTHTHHTHTTTTTHTHTTHHTHTHHHTHTHHTHTHHTTTHH
I have little knowledge how to do this, so I looked into what others have done. Apparently Multi-row INSERT is not supported. Some sources say the only way to insert several rows in a batch is use a Select statement. How would I achieve this?
Assuming the database and table is already created, what code could I use in a C program to insert all this data into SQLite?
/* This file was mechanically generated from tests/check-pcg32.c */
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdbool.h>
#include <time.h>
#include <string.h>
#include "pcg_basic.h"
int main(int argc, char** argv)
{
// Read command-line options
int rounds = 1000;
bool nondeterministic_seed = false;
int round, i;
++argv;
--argc;
if (argc > 0 && strcmp(argv[0], "-r") == 0) {
nondeterministic_seed = true;
++argv;
--argc;
}
if (argc > 0) {
rounds = atoi(argv[0]);
}
// In this version of the code, we'll use a local rng, rather than the
// global one.
pcg32_random_t rng;
// You should *always* seed the RNG. The usual time to do it is the
// point in time when you create RNG (typically at the beginning of the
// program).
//
// pcg32_srandom_r takes two 64-bit constants (the initial state, and the
// rng sequence selector; rngs with different sequence selectors will
// *never* have random sequences that coincide, at all) - the code below
// shows three possible ways to do so.
if (nondeterministic_seed) {
// Seed with external entropy -- the time and some program addresses
// (which will actually be somewhat random on most modern systems).
// A better solution, entropy_getbytes, using /dev/random, is provided
// in the full library.
pcg32_srandom_r(&rng, time(NULL) ^ (intptr_t)&printf,
(intptr_t)&rounds);
} else {
// Seed with a fixed constant
pcg32_srandom_r(&rng, 42u, 54u);
}
printf("pcg32_random_r:\n"
" - result: 32-bit unsigned int (uint32_t)\n"
" - period: 2^64 (* 2^63 streams)\n"
" - state type: pcg32_random_t (%zu bytes)\n"
" - output func: XSH-RR\n"
"\n",
sizeof(pcg32_random_t));
for (round = 1; round <= rounds; ++round) {
printf("Round %d:\n", round);
/* Make some 32-bit numbers */
printf(" 32bit:");
for (i = 0; i < 6; ++i)
printf(" 0x%08x", pcg32_random_r(&rng));
printf("\n");
/* Toss some coins */
printf(" Coins: ");
for (i = 0; i < 100; ++i)
printf("%c", pcg32_boundedrand_r(&rng, 2) ? 'H' : 'T');
printf("\n");
printf("\n");
}
return 0;
}

Answer 1

I guess I would start with a simple approach and if you need to access results based on rounds and tosses, your table in the database could consist of three fields, e.g. round, toss and result.
To create the database and the table, you could use the command line program sqlite3 as follows:
sqlite3 random.sqlite
Then enter the following command at the command prompt:
CREATE TABLE experiment (round INT, toss INT, result CHAR(1));
Now you have created a database random.sqlite and a table experiment.
How to fill this table from C?
One way would be:
open db
create a prepared insert statement
start a transaction
in a loop:
bind values to parameters
run the SQL
reset prepared statement
end transaction
finalize the statement and close the db to avoid resource leaks
A simple example of the flow described could look like this:
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "sqlite3.h"
void exit_with_error(sqlite3 *db, const char * msg) {
fprintf(stderr, "%s: %s\n", msg, sqlite3_errmsg(db));
sqlite3_close(db);
exit(1);
}
char *pathToDB = "<a path to random.sqlite>";
sqlite3 *open_db(void);
sqlite3_stmt *prepeare_stmt(sqlite3 *db);
void close_db(sqlite3 *db, sqlite3_stmt *stmt);
int main() {
sqlite3 *db = open_db();
sqlite3_stmt *stmt = prepeare_stmt(db);
if(sqlite3_exec(db, "BEGIN TRANSACTION", NULL, NULL, NULL) != SQLITE_OK) {
exit_with_error(db, "begin transaction failed");
}
char *result = "H";
for(int round = 0; round < 100; round++) {
for(int toss = 0; toss < 100; toss++) {
//for a short test simply output alternately "H" and "T"
result = strcmp(result, "H") == 0 ? "T" : "H";
//bind values to parameters
sqlite3_bind_int(stmt, 1, round);
sqlite3_bind_int(stmt, 2, toss);
sqlite3_bind_text(stmt, 3, result, -1, SQLITE_STATIC);
//run the SQL
if (sqlite3_step(stmt) != SQLITE_DONE) {
exit_with_error(db, "insert failed");
}
//reset prepared statement to be able to bind new values in next loop pass
if (sqlite3_reset(stmt) != SQLITE_OK) {
exit_with_error(db, "reset failed");
}
}
}
if(sqlite3_exec(db, "END TRANSACTION", NULL, NULL, NULL) != SQLITE_OK) {
exit_with_error(db, "end transaction failed");
}
//finalize the stmt and close db to avoid resource leaks
sqlite3_finalize(stmt);
sqlite3_close(db);
return 0;
}
sqlite3 *open_db(void) {
sqlite3 *db;
if (sqlite3_open(pathToDB, &db) != SQLITE_OK) {
exit_with_error(db, "can't open db: ");
}
return db;
}
sqlite3_stmt *prepeare_stmt(sqlite3 *db) {
sqlite3_stmt *stmt;
//create a prepared statement
int rc = sqlite3_prepare_v2(db, "INSERT INTO experiment VALUES (?1,?2,?3)", -1, &stmt, 0);
if (rc != SQLITE_OK) {
exit_with_error(db, "failure preparing insert");
}
return stmt;
}
Note: Instead of using random values, the code simply outputs 'T' and 'H' alternately to have a simple test case.
After executing the program, you can take a look at the stored values with the command line as follows:
sqlite3 random.sqlite
At the sqlite command prompt you can enter:
SELECT * FROM experiment;
The following should then be output in the console:
0|0|T
0|1|H
0|2|T
...
99|97|H
99|98|T
99|99|H
To get the value for the third toss in the first round you would issue the following sql statement from the command prompt:
SELECT * from experiment WHERE round=0 and toss=2;
that would output something like this on the console:
0|2|T