In general, the library returns a StatusOr if an error is possible. Some functions return objects that are not wrapped in a StatusOr<T> but will themselves return a StatusOr<T> 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 spanner = ::google::cloud::spanner;
[](spanner::Client client) {
auto rows = client.Read("Albums", spanner::KeySet::All(), {"AlbumTitle"});
// The actual type of `row` is google::cloud::StatusOr<spanner::Row>, but
// we expect it'll most often be declared with auto like this.
for (auto const& row : rows) {
// Use `row` like a smart pointer; check it before dereferencing
if (!row) {
// `row` doesn't contain a value, so `.status()` will contain error info
std::cerr << row.status();
break;
}
// The actual type of `song` is google::cloud::StatusOr<std::string>, but
// again we expect it'll be commonly declared with auto as we show here.
auto song = row->get<std::string>("AlbumTitle");
// Instead of checking then dereferencing `song` as we did with `row`
// above, here we demonstrate use of the `.value()` member, which will
// return a reference to the contained `T` if it exists, otherwise it
// will throw an exception (or terminate if compiled without exceptions).
std::cout << "SongName: " << song.value() << "\n";
}
}
[[["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 2025-08-22 UTC."],[[["\u003cp\u003eThis document details the error handling procedures for the Spanner C++ library, with version 2.37.0-rc being the latest release candidate and 2.16.0 being the documented version at the time of writing.\u003c/p\u003e\n"],["\u003cp\u003eThe library predominantly uses \u003ccode\u003eStatusOr<T>\u003c/code\u003e to manage potential errors, functioning like a smart pointer that either holds a value of type \u003ccode\u003eT\u003c/code\u003e or a \u003ccode\u003eStatus\u003c/code\u003e object detailing an error.\u003c/p\u003e\n"],["\u003cp\u003eDevelopers should verify if a \u003ccode\u003eStatusOr<T>\u003c/code\u003e object contains a value using methods like \u003ccode\u003e.ok()\u003c/code\u003e or \u003ccode\u003eoperator bool()\u003c/code\u003e before attempting to access the value to prevent errors, and if it does not contain a value you can access the \u003ccode\u003eStatus\u003c/code\u003e error information with \u003ccode\u003e.status()\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eAlternatively, the \u003ccode\u003e.value()\u003c/code\u003e member function can be utilized to retrieve the contained value, but it will either throw a \u003ccode\u003eRuntimeStatusError\u003c/code\u003e exception or terminate the program if the object does not hold a value.\u003c/p\u003e\n"],["\u003cp\u003eThe library has other functions that are not wrapped in a \u003ccode\u003eStatusOr<T>\u003c/code\u003e but that will return a \u003ccode\u003eStatusOr<T>\u003c/code\u003e to signal an error, such as wrappers for asynchronous operations that return \u003ccode\u003efuture<StatusOr<T>>\u003c/code\u003e.\u003c/p\u003e\n"]]],[],null,[]]
