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POHow to log exceptional situations in C++?
 

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  1. POHow to log exceptional situations in C++?
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    <p>When writing a function, my implementation very frequently looks like this:</p> <ul> <li>Call a subfunction</li> <li>If this subfunction fails to execute (because of an exceptional situation): log this failure and abort the current function</li> <li>Otherwise continue calling other subfunctions, which in turn can fail</li> </ul> <p>A crucial part is the logging. Every function that fails should add a short description to the log. This way, at the level where the exception is handled, the user can be shown a detailed error message.</p> <p>For example, consider an application where a new user account can be created, and there is a problem with the database connection. The following inverse stack trace results:</p> <ul> <li>SQLDriverConnect() -> "SQLDriverConnect error: Data source not found and no default driver specified"</li> <li>OpenDatabaseConnection() -> "Failed to open database connection" </li> <li>CreateUser() -> "Failed to create the new user"</li> <li>ValidateAndSaveNewUserAccount() -> "Failed to save the user profile"</li> <li>Catch the exception and show the logged messages to the user</li> </ul> <p>Using the exceptions feature, I would implement this as follows:</p> <pre><code>void CreateUser() { try { OpenDatabaseConnection(); } catch(std::exception&amp; e) { e.AddLog("Failed to create the new user"); throw; } //... } </code></pre> <p>Using a simple return value, I'd write the following: </p> <pre><code>bool CreateUser(Log&amp; log) { if (!OpenDatabaseConnection(log)) { log.Add("Failed to create the new user"); return false; } //... return true; } </code></pre> <p>I find both implementations equally good. Therefore, I don't see much advantage in using exceptions. I am well aware that exception handling is generally considered a useful feature, but I don't really understand why. A long time ago, I used exception handling extensively, but I didn't see the big advantage, so now I never use them anymore. Hence my questions:</p> <ul> <li>Using exceptions, how can this be implemented in C++ more concisely?</li> <li>If not, what is then the advantage of throwing exceptions over returning an "is successful" boolean?</li> </ul> <p><b>Note:</b> I use the term <b>logging</b> as "collecting an explanation of what went wrong, so it can be presented to the user later on". I'd rather not store that explanation in a global collection of log messages (in memory, in a file or in a database), as it directly describes the specific exception. </p> <p><b>Update</b>: Thanks for you responses so far. I understand that exceptions are only useful if the user doesn't need detailed feedback on what went wrong. (Please correct me if I misinterpreted this.)</p>
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    1. COQuestion about your logging scheme. Whenever a function reports failure it logs an error, right? What with situations when in some contexts failure is an error and in some it isn't? Like when in some situations SQLDriverConnect() can fail (and OpenDatabaseConnection()) and it's not an error for calling code, just a signal to try another connection. Will it write the failure to log as well? I'm just worried that logs will become noisy which will hide real problems when they appear.
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      1. USTomek Szpakowicz
    2. CO@tomekszpakowicz: I meant to log the error messages in memory. It is up to the exception handler to decide whether they should be written to disk, show in a dialog, or simply ignored.
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      1. USDimitri C.
    3. COThis may be useful to you, even if not directly related to your question: http://www.ddj.com/cpp/201804215
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