Incorrect query result with `use` and `into` into vector, at least for sqlite3.

[tamaskenez]

At least with the sqlite3 backend, when a query is created both with use bindings and with into into a vector, the result is incorrect if the vector's size is 1.

In the test below, the SELECT statement returns one row. If the vector is resized to 2, the result is correct. If it's resized to 1, although it's just enough, it will be cleared.

#include <soci/soci.h>
#include <soci/sqlite3/soci-sqlite3.h>
#include <filesystem>
#include <cassert>
#include <vector>

int main2() {
    std::filesystem::remove("test.db");
    soci::session s(*soci::factory_sqlite3(), "test.db");
    s << "CREATE TABLE test ( key PRIMARY KEY )";
    s << "INSERT INTO test(key) VALUES('foo')";

    std::vector<std::string> v;
    for(auto N: {2u, 1u}) {
        v.resize(N);
        s << "SELECT key FROM test WHERE key = ?", soci::use(std::string("foo")), soci::into(v);
        assert(v.size() == 1 && v[0] == "foo"); // Fails if N == 1, v.size() will be 0
    }
    return 0;
}

[vadz]

One thing I can say without testing this code is that your use of temporary string with use seems to be incorrect, you should see "use after free" errors with ASAN.

[tamaskenez]

@vadz thanks for looking into this, I fixed it, still hits the assertion:

#include <soci/soci.h>
#include <soci/sqlite3/soci-sqlite3.h>
#include <cassert>
#include <filesystem>
#include <vector>

int main() {
    std::filesystem::remove("test.db");
    soci::session s(*soci::factory_sqlite3(), "test.db");
    s << "CREATE TABLE test ( key PRIMARY KEY )";
    s << "INSERT INTO test(key) VALUES('foo')";

    std::vector<std::string> v;
    for (auto N : {2u, 1u}) {
        v.resize(N);
        const std::string foo("foo");
        s << "SELECT key FROM test WHERE key = ?", soci::use(foo), soci::into(v);
        assert(v.size() == 1 && v[0] == "foo");  // Fails if N == 1, v.size() will be 0
    }
    return 0;
}