This rule raises an issue when a generic exception (such as std::exception, std::logic_error or
std::runtime_error) is thrown.
Why is this an issue?
Throwing generic exceptions such as std::exception, std::logic_error and std::runtime_error will have a
negative impact on any code trying to catch these exceptions.
From a consumer perspective, it is generally a best practice to only catch exceptions you intend to handle. Other exceptions should ideally not be
caught and let propagate up the stack trace so that they can be dealt with appropriately. When a generic exception is thrown, it forces consumers to
catch exceptions they do not intend to handle, which they then have to re-throw.
Besides, when working with a generic type of exception, the only way to distinguish between multiple exceptions is to check their message, which is
error-prone and difficult to maintain. Legitimate exceptions may be unintentionally silenced and errors may be hidden.
For instance, in the following code, the fact that checkState throws a generic exception leads us to catch a permission error that
shouldn’t have been caught:
void openFile(File& file) {
if (!has_permissions(file)) {
throw std::invalid_argument("Couldn't open file");
}
// ...
}
void checkState(File const& file) {
if (!file.is_valid()) {
throw std::exception(); // Noncompliant
}
// ...
}
void test(File file) {
try {
openFile(file);
checkState(false);
closeFile(file);
} catch (std::exception& s) {
// If we don't have the correct permissions to open, the
// invalid_argument exception will be caught and we will try closing a
// file that was never opened
closeFile(file);
}
}
Therefore, throwing the most specific exception possible is recommended so consumers can handle it intentionally.
How to fix it
To fix this issue, make sure to throw specific exceptions that are relevant to the context in which they arise. It is recommended to either:
- Throw a subtype of
std::exception when one matches. For instance, std::invalid_argument could be raised when an
unexpected argument is provided to a function.
- Define a custom exception type that derives from
std::exception or one of its subclasses.
Code examples
Noncompliant code example
#include <stdexcept>
void checkState(S state) {
if (!state.is_valid()) {
throw std::exception("State is invalid"); // Noncompliant: this will be difficult for consumers to handle
}
// ...
}
Compliant solution
The solution below involves throwing std::invalid_argument, which is an appropriate exception type for this situation:
#include <stdexcept>
void checkState(S state) {
if (!state.is_valid()) {
throw std::invalid_argument("State is invalid"); // Compliant
}
// ...
}
Alternatively, one can define a custom invalid_state exception that can be caught specifically:
struct invalid_state : public std::exception {};
void checkState(S state) {
if (!state.is_valid()) {
throw invalide_state(); // Compliant
}
// ...
}
Resources
Standards
External coding guidelines
Related rules
- S1181 - Generic exceptions should not be caught
