Question

I’m starting from the bottom-up to learn iPad development after 15 years with Cold Fusion. I’m getting comfortable with Ansi C and xCode, but am stumped taking the next step with SQLite.

I’ve built a database (Airports.sqlite) with razorSQL and installed it in the same directory as main.c where I’ve also installed the amalgamated sqlite3.h and sqlite3.h files.

Everything compiles OK, but I get the following message when I Run…

Error in select statement select Length from Runways order by Length desc limit 5 [no such table: Runways].

The database definitely has the Runways table in it. Can someone set me straight? Here’s the code:

---

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "sqlite3.h"
#include "weightbalance.h"

sqlite3* db;
int first_row;

int select_callback(void *p_data, int num_fields, char **p_fields, char **p_col_names) {

    int i;
    int *p_rn = (int*)p_data;

    if (first_row) {
        first_row = 0;

        for(i=0; i < num_fields; i++) {
            printf("%20s", p_col_names[i]);
        }
        printf("\n");
        for(i=0; i< num_fields*20; i++) {
            printf("=");
        }
        printf("\n");
    }

    (*p_rn)++;

    for(i=0; i < num_fields; i++) {
        printf("%20s", p_fields[i]);
    }

    printf("\n");
    return 0;
}


void select_stmt(const char* stmt) {
    char *errmsg;
    int   ret;
    int   nrecs = 0;

    first_row = 1;

    ret = sqlite3_exec(db, stmt, select_callback, &nrecs, &errmsg);

    if(ret!=SQLITE_OK) {
        printf("Error in select statement %s [%s].\n", stmt, errmsg);
    }
    else {
        printf("\n   %d records returned.\n", nrecs);
    }
}

void sql_stmt(const char* stmt) {
    char *errmsg;
    int   ret;

    ret = sqlite3_exec(db, stmt, 0, 0, &errmsg);

    if(ret != SQLITE_OK) {
        printf("Error in statement: %s [%s].\n", stmt, errmsg);
    }
}

int main() {
    sqlite3_open("Airports.sqlite", &db);

    if(db == 0) {
        printf("Could not open database.");
        return 1;
    }

    printf("\nSelecting Airports with the longest runways.\n\n");
    select_stmt("select Length from Runways order by Length desc limit 5");

    sqlite3_close(db);
    return 0;
}

Answer 1

Most likely, the file “Airports.sqlite” opened in main() is not the one you think it is. Without path information, sqlite3_open() will just open the file in the current working directory.

As a debug step, add “printf(getwd(NULL))” just before your sqlite3_open() statement. Then you’ll know whether you’re opening your existing database or just creating a new, empty one that is missing your table.

Also, since you’re using Xcode, you can just pass the path to your database as a command-line parameter (argv). In Xcode 4, choose Product->Edit Scheme. In the “run” section, add the path to “Arguments Pass On Launch”. Then you can just pass argv[1] to your sqlite3_open().