In general, the library returns a StatusOr if an error is possible. Some functions return objects that are not wrapped in a StatusOr<> but will themselves return a StatusOr<> to signal an error. For example, wrappers for asynchronous operations return future<StatusOr<T>>.
Applications should check if the StatusOr<T> contains a value before using it, much like how you might check that a pointer is not null before dereferencing it. Indeed, a StatusOr<T> object can be used like a smart-pointer to T, with the main difference being that when it does not hold a T it will instead hold a Status object with extra information about the error.
You can check that a StatusOr<T> contains a value by calling the .ok() method, or by using operator bool() (like with other smart pointers). If there is no value, you can access the contained Status object using the .status() member. If there is a value, you may access it by dereferencing with operator*() or operator->(). As with all smart pointers, callers must first check that the StatusOr<T> contains a value before dereferencing and accessing the contained value. Alternatively, callers may instead use the .value() member function which is defined to throw a RuntimeStatusError if there is no value.
Example
namespace pubsub = ::google::cloud::pubsub;
[](pubsub::TopicAdminClient client, std::string const& project_id) {
// The actual type of `topic` is
// google::cloud::StatusOr<google::pubsub::v1::Topic>, but
// we expect it'll most often be declared with auto like this.
for (auto& topic : client.ListTopics(project_id)) {
// Use `topic` like a smart pointer; check it before de-referencing
if (!topic) {
// `topic` doesn't contain a value, so `.status()` will contain error
// info
std::cerr << topic.status() << "\n";
break;
}
std::cout << topic->DebugString() << "\n";
}
}
See Also
google::cloud::future for more details on the type returned by asynchronous operations.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Missing the information I need","missingTheInformationINeed","thumb-down"],["Too complicated / too many steps","tooComplicatedTooManySteps","thumb-down"],["Out of date","outOfDate","thumb-down"],["Samples / code issue","samplesCodeIssue","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-07-02 UTC."],[[["This document details the error handling process for the Google Cloud Pub/Sub C++ client library, which commonly returns a `StatusOr` object when an error might occur."],["Users should verify that a `StatusOr` object contains a value using methods like `.ok()` or `operator bool()` before attempting to access the underlying data, similar to using a smart pointer."],["If an error is present, the `Status` object containing error details can be retrieved using the `.status()` method, while the `.value()` method will throw a `RuntimeStatusError` if no value is present, or terminate the program if exceptions are disabled."],["The provided code example showcases how to properly iterate through a list of topics using a `StatusOr` object, demonstrating how to check for errors before accessing the data."],["The document also provides links to documentation, such as to the [`google::cloud::future`](https://cloud.google.com/cpp/docs/reference/common/latest/classgoogle_1_1cloud_1_1future.html) page, for additional information regarding asynchronous operations."]]],[]]
