c语言打开sql数据库

#include <stdio.h>
#include <stdlib.h>
#include <sqlca.h>

void check_error() {
    if (sqlca.sqlcode != 0) {
        printf("SQL error: %s\n", sqlca.sqlerrm.sqlerrmc);
        exit(1);
    }
}

int main() {
    EXEC SQL BEGIN DECLARE SECTION;
    char username[50];
    char password[50];
    EXEC SQL END DECLARE SECTION;

    printf("Enter username: ");
    scanf("%s", username);
    printf("Enter password: ");
    scanf("%s", password);

    EXEC SQL CONNECT TO mydatabase USER username USING password;
    check_error();

    EXEC SQL SELECT * FROM users WHERE username = :username;
    check_error();

    EXEC SQL FETCH NEXT FROM users INTO :username;
    while (sqlca.sqlcode == 0) {
        printf("Username: %s\n", username);
        EXEC SQL FETCH NEXT FROM users INTO :username;
    }

    EXEC SQL DISCONNECT ALL;
    check_error();

    return 0;
}