error: incompatible types when initializing type 'char *' using type 'double' - sql

Question

Good afternoon,
I've got this code below:
double bd_sacar_imc(double altura, double peso) {
sqlite3 *db;
char *zErrMsg = 0;
int rc;
char *sql = ("SELECT %lf/(%lf * %lf);", peso, altura, altura);
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
if (rc != SQLITE_OK) {
fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
return 0;
} else {
fprintf(stdout, "Consulta creada con exito\n");
return peso / (altura * altura);
}};
However, I get this error:
..\BD\bd.c:170:14: error: incompatible types when initializing type 'char *' using type 'double' char *sql = ("SELECT %lf /( %lf * %lf);", peso, altura, altura);
What might be happening?

Answer 1

It looks like you are trying to build a string. For that you can use snprintf.
char sql[64];
int size = snprintf(sql, 64, "SELECT %lf/(%lf * %lf);", peso, altura, altura);
Note that I kept the return value. This is to handle any future error where you modify a statement in a way that might result in buffer overflow or other error. You can probably just deal with this by using a debug assertion, as this pre-sized string should be large enough to hold the intended SQL.
if (size < 0 || size >= 64) {
assert(0);
return 0;
}
However, since you are using sqlite library, you should instead use the proper methods to prepare a statement and bind values to it, rather than inserting the values into the string yourself.