我有一个大约4.8mb的字符串（只包含base64个karakter，proven）。
但是，当我尝试使用以下语句绑定字符串时：

sqlPrepared_userdb_test->setString(1, Content); //Content is approximately 4.8MB

mysql返回：

Incorrect string value: '\xF7/\x00\x00\xF0...' for column 'Content' at row 1 (error code: 1366, State: HY000)

但是，当我将内容字符串直接包含在查询（内联）中时，插入成功。我使用的内联查询（跳过了中间部分内容）：

INSERT INTO Test (Content) Values('ajHEHAU......8837x=='); //Content is approximately 4.8MB

为什么绑定失败，但内联完全相同的字符串成功？
编辑：

Log("Inserting content!", false, "Debug");

for (auto& Char : Content) {
    if (Char >= 'a' && Char <= 'z') {
        }
    else if (Char >= 'A' && Char <= 'Z') {
        }
    else if (Char >= '0' && Char <= '9') {
        }
    else if (Char == '+') {
        }
    else if (Char == '/') {
        }
    else if (Char == '=') {
        }
    else {
        string Message = "Char in content: ";
        Message += Char;
        Message += " is not allowed!";
        Error(Message);
        // NO ERROR REPORTED HERE. CONTENT STRING SEEMS GOOD
        }
    }

try {
    sqlPrepared_userdb_test = mysqli_userdb->prepareStatement("INSERT INTO Test (Content) VALUES(?)");
    sqlPrepared_userdb_test->setString(1, Content);
    sqlPrepared_userdb_test->executeUpdate();
    }
catch (sql::SQLException &e) {
    Message = "Database test error: ";
    Message += e.what();
    Message += " (error code: ";
    Message += IntToString(e.getErrorCode());
    Message += ", State: ";
    Message += e.getSQLState();
    Message += ")";
    Log(Message, false, "Error");
    Error("Database");

    // CATCH TRIGGERS

    }

outfile.close();

sqlPrepared_userdb->setString(ParamOffset++, Content);