蒟蒻对cmp函数的使用有些疑惑

已在代码块中标出

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef struct stu stu;
struct stu{
	ll idx; 
	string name;
	ll x,y,z;
};
bool cmp(stu ob1,stu ob2){
	if(ob1.x==ob2.x&&ob1.y==ob2.y&&ob1.z==ob2.z)return 1//困惑的地方
	else if(ob1.x==ob2.x&&ob1.y==ob2.y)return ob1.z<ob2.z;
	else if(ob1.x==ob2.x)return ob1.y<ob2.y;
	else return ob1.x<ob2.x;
}
void solve(){
	ll n;cin>>n;
	vector<stu>v;
	for(ll i=0;i<n;++i){
		string x;
		ll y,z,e;cin>>x>>y>>z>>e;
		v.push_back({i,x,y,z,e});
	}
	sort(v.begin(),v.end(),cmp);
	for(auto &i:v)cout<<i.name<<"\n";
}
int main(){
	ll T=1;
	while(T--)solve();
	return 0;
}

题目要求后输入的先输出,我以为cmp返回1就是不交换,也就是达到后输入的先输出的效果

然而#5测试点WA了,

后来将该处代码添加了顺序的比较,改为:

if(ob1.x==ob2.x&&ob1.y==ob2.y&&ob1.z==ob2.z)return ob1.idx>ob2.idx;

ac通过了.

请问各位dalao,cmp的含义到底是什么呢?