C++中依据结构体成员变量对结构体向量进行排序的技术问询

Hey there! Let's fix your sorting issue quickly. You don't need those iterators pointing directly to the value_t members—instead, we can tell std::sort exactly how to compare your BarItem objects based on their value field. Here's how to do it:

1. Core Idea: Custom Comparators for std::sort #

The std::sort function lets you pass a custom rule (a comparator) to define the order of elements. For your goal (sorting so larger value values come first), we just need to write logic that checks if one BarItem's value is bigger than another's.

2. Method 1: Using a Standalone Comparison Function #

First, add a helper function that compares two BarItems. Make sure to include the <algorithm> header for std::sort:

#include <algorithm>

// Returns true if a should come before b (descending order by value)
bool compareByValueDesc(const bcra::BarChart::BarItem& a, const bcra::BarChart::BarItem& b) {
    return a.value > b.value;
}

Then use this function in your main code when calling sort:

int main() {
    bcra::BarChart m_barChart; // Fix: reference the bcra namespace!
    // ... (your file reading and bar_s population code) ...

    // Sort bar_s with our custom rule
    std::sort(bar_s.begin(), bar_s.end(), compareByValueDesc);
}

3. Method 2: Using a Lambda Expression (More Concise) #

If you don't want a separate function, you can pass a lambda directly to std::sort—this is cleaner for simple comparisons:

int main() {
    bcra::BarChart m_barChart;
    // ... (your existing code) ...

    // Sort with an inline lambda
    std::sort(bar_s.begin(), bar_s.end(), 
        [](const bcra::BarChart::BarItem& a, const bcra::BarChart::BarItem& b) {
            return a.value > b.value; // Larger values come first
        }
    );
}

4. Quick Fixes for Your Code #

• Namespace Correction: Your BarChart class lives in the bcra namespace, so you need to write bcra::BarChart (not just BarChart) in main to avoid compilation errors.
• Skip the Value Iterators: std::sort works with iterators to your BarItem objects directly—you don't need to point to the value member itself. The comparator handles accessing that field for you.

内容的提问来源于stack exchange，提问作者diniz junior