c-program sqlite3 check if table exists

Question

I've been trying to write a function that takes a name as parameter and checks a database to see if there exists a table with that name, but for some reason it keeps failing. Maybe someone can push me in the right direction here. Thanks!!!

Here's the functions i have:

int check_table(char tbl_name[])
{
    sqlite3 *db;
    char *err_msg = 0;
    char sql_query[1024];

    printf("checking for: %s\n", tbl_name);


    int rc = sqlite3_open(db_name, &db);

    if (rc != SQLITE_OK)
    {
        fprintf(stderr, "Cannot open database: %s\n", 
        sqlite3_errmsg(db));
        sqlite3_close(db);

        return 1;
    }

    // assemble string
    snprintf(sql_query,sizeof(sql_query), "SELECT name FROM sqlite_master WHERE type='table' AND name=\'%s\'", tbl_name);


    rc = sqlite3_exec(db, sql_query, callbackcheck, 0, &err_msg);

    if (rc != SQLITE_OK )
    {
        fprintf(stderr, "Failed to select data\n");
        fprintf(stderr, "SQL error: %s\n", err_msg);

        sqlite3_free(err_msg);
        sqlite3_close(db);

        return 1;
    } 
    sqlite3_close(db);

    // needs some work here 
    return 1; // table does exists
    //return 0; // table does not exists
}



    int callbackcheck(void *NotUsed, int argc, char **argv, char **azColName)
{
    NotUsed = 0;
    printf("argc: %s - argv: %s - azColName: %s", argc, argv, azColName);

    for (int i = 0; i < argc; i++)
    {
        printf("%s\n", argv[i] ? argv[i] : "NULL");
    }
    return 0;
}

My problem lies in how to get a True/False returned, so ideally i would call the function like so: bool tb_is_there = check_table("some_tbl"); then I can return tb_is_there;

I hope that makes sense

If return value is the only problem, C99 has bool macros which you can use. Include stdbool.h and If table exists in DB return true if not return false. — Ravi, Mar 30 '18 at 05:18
Possible duplicate of [SQLite3 C interface: how to determine existence of a table](https://stackoverflow.com/questions/22931629/sqlite3-c-interface-how-to-determine-existence-of-a-table) — iammilind, Sep 04 '19 at 05:05

score 1 · Answer 1 · answered Mar 30 '18 at 06:40

The callback is hard to use if you want to do anything but print out the data. In the general case, the only useful way to use sqlite3_exec() is to replace it with sqlite3_prepare_v2()/sqlite3_bind_*()/sqlite3_step()/sqlite3_finalize() calls so that you can read the data in the same place where you actually need to handle it:

sqlite3_stmt *stmt;
const char *sql = "SELECT 1 FROM sqlite_master where type='table' and name=?";

int rc = sqlite3_prepare_v2(db, sql, -1, &stmt, NULL);
if (rc != SQLITE_OK) {
    print("error: ", sqlite3_errmsg(db));
    return;
}
sqlite3_bind_text(stmt, 1, tbl_name, -1, SQLITE_TRANSIENT);

rc = sqlite3_step(stmt);
bool found;
if (rc == SQLITE_ROW)
    found = true;
else if (rc == SQLITE_DONE)
    found = false;
else {
    print("error: ", sqlite3_errmsg(db));
    sqlite3_finalize(stmt);
    return;
}

sqlite3_finalize(stmt);
return found;

score 0 · Answer 2 · answered Oct 19 '22 at 23:20

Try this : https://www.sqlite.org/c3ref/table_column_metadata.html

int rc = sqlite3_table_column_metadata(db,NULL,tbl_name,NULL,NULL,NULL,NULL,NULL,NULL);

if (rc != SQLITE_OK )
{
    fprintf(stderr, "Table did not exist \n");
} 
else
{
    fprintf(stdout, "Table exist \n");
}

c-program sqlite3 check if table exists

2 Answers2