使用std::sort排序自定义ShapeDescriptor对象vector报错，求排查方向

Hey there, let's walk through the most likely issues causing your sorting errors, since you suspect the comparison logic is the root of the problem. Here are key points to check:

1. Incomplete Lambda Syntax #

Your code snippet cuts off at retur...—if your lambda doesn't finish the comparison expression, that's an immediate syntax error. A valid, complete comparator lambda should look something like this:

std::sort(bins.begin(), bins.end(), [](const ShapeDescriptor& a, const ShapeDescriptor& b) {
    // Replace with your actual property comparison logic
    return a.getBoundingBoxWidth() < b.getBoundingBoxWidth();
});

Double-check that you've finished writing the return statement with a valid boolean expression.

2. Unnecessary Copies (and Missing Copy Constructors) #

Your current lambda uses value parameters (ShapeDescriptor a, ShapeDescriptor b), which means every comparator call will make a full copy of your ShapeDescriptor objects. This can cause two big issues:

• If ShapeDescriptor has a deleted copy constructor, or lacks implicit copying support for its members, you'll get a compile error.
• Even if copying works, it's inefficient for large or complex objects.

Fix this by switching to const references to avoid copies and ensure you don't modify the objects during comparison:

[](const ShapeDescriptor& a, const ShapeDescriptor& b) { ... }

3. Violating Strict Weak Ordering #

std::sort requires the comparator to enforce strict weak ordering—break these rules, and you'll get undefined behavior (crashing, incorrect sorting, or weird runtime glitches). The non-negotiable rules are:

• An object must never be "less than" itself (no a < a allowed).
• If a < b is true, then b < a must be false.
• If a < b and b < c, then a < c must be true.
• If a isn't less than b and b isn't less than a, a and b are considered equivalent (their relative order in the sorted vector is unspecified).

For example, using <= instead of < in your comparator directly breaks this rule and will cause problems.

4. Accessing Private/Protected Members #

If your comparator tries to access private or protected members of ShapeDescriptor, the lambda won't have permission to do so. To fix this:

• Add public getter methods for the properties you need to compare (e.g., a.getArea() instead of directly accessing a.area).
• If you need direct member access, declare the lambda as a friend of ShapeDescriptor (though getters are usually the cleaner approach).

Next Step: Share Full Error Logs #

To pinpoint the exact issue, sharing the full compiler error messages would be incredibly helpful. For example:

• Compile errors might explicitly mention missing copy constructors, invalid syntax, or inaccessible members.
• Runtime errors could hint at a broken strict weak ordering causing memory issues.

内容的提问来源于stack exchange，提问作者Mohamad Alhaddad