Question

问题出在块内：

check_sort(l.begin(), l.end(), "list");
time_insert(insert_list, data);
check_sort(s.begin(), s.end(), "set");
time_insert(insert_set, data);
check_sort(v.begin(), v.end(), "vector");
time_insert(insert_vector, data);

错误表明变量未在范围内声明，但l，s，v不应该是通用变量吗？我做错了什么。

#include <cmath>
#include <iterator>
#include <iostream>
#include <iomanip>
#include <vector>
#include <ctime>
#include <list>
#include <set>
#include <algorithm>
#include <cstdlib>

using namespace std;

typedef void Inserter(vector<double>);

vector<double> gen_data(int num_elts);
void insert_list(vector<double> data);
void insert_set(vector<double> data);
void insert_vector(vector<double> data);

void time_insert( Inserter inserter, vector<double> data);

template <class Iter> bool is_sorted(Iter first, Iter last);
template <class Iter> void check_sort(Iter first, Iter last, string cont_kind);

int main() {
    srand(time(0));// initialize random number generator
    cout << "How many elements for container? ";
    int num_elts = 0;

    while (cin >> num_elts) {
    if (num_elts <= 0)
        cout << "Error, should be > 1";
    else {
        vector<double> data = gen_data(num_elts);

        check_sort(l.begin(), l.end(), "list");
        time_insert(insert_list, data);
        check_sort(s.begin(), s.end(), "set");
        time_insert(insert_set, data);
        check_sort(v.begin(), v.end(), "vector");
        time_insert(insert_vector, data);

    }
    cout << "\nHow many elements for next container? ";

    }
    return 0;

} 
void time_insert( Inserter inserter, vector<double> data) {
    clock_t t1 = clock();
    if (t1 == clock_t(-1)) { //if clock() doesn’t work
    cerr << "sorry, no clock\n";
    exit(1);
    }

    inserter(data);
    clock_t t2 = clock(); 
    if (t2 == clock_t(-1)) {
    cerr << "sorry, clock overflow\n";

    exit(2);
    }

    cout << "Elapsed time: " << fixed << setprecision(2)
     << double(t2-t1)/CLOCKS_PER_SEC << " seconds\n";

}

class Larger_than { 
    double v;
public: 
    Larger_than(double vv) : v(vv){}
    bool operator()(double x) const {return x>v;}
};

// Sorts and then inserts data into a list
void insert_list(vector<double> data)
{
    list<double> l;
    for(int i=0; i < data.size(); i++){
    list<double>::iterator p = find_if(l.begin(),l.end(), Larger_than(data[i]));
    l.insert(p, data[i]);
    }
} 
// Sorts and then inserts data into a list
void insert_set(vector<double> data)
{
    set<double> s; 
    for(int i=0; i < data.size(); i++){
    set<double>::iterator p = find_if(s.begin(),s.end(), Larger_than(data[i]
                          ));
    s.insert(p, data[i]);
    }
} 
// Sorts and then inserts data into a list 
void insert_vector(vector<double> data)
{
    vector<double> v; 
    for(int i=0; i < data.size(); i++){
    vector<double>::iterator p = find_if(v.begin(),v.end(), Larger_than(data
                                        [i]));
    v.insert(p, data[i]);
    }
} 

// generate num_elts random numbers in the range [0.0, 1.0), 
// which are returned in a vector

vector<double> gen_data (int num_elts) 
{
    vector<double> result; 
    for (int i = 0; i < num_elts; i++) {
    double datum = 1.0*rand()/RAND_MAX; 
    result.push_back(datum);
    }
    return result;
}

// is container spanned by [from, last) sorted?  
template <class Iter> bool is_sorted(Iter first, Iter last)  
{  
    Iter next = first;                   // next element  
    for (next++; next != last; next++, first++) {  
    if (*first > *next)  
        return false;  
    }  
    return true;  
}  

// prints a msg describing container kind, as well as whether container  
// spanned by [from, last) is sorted  
template <class Iter> void check_sort(Iter first, Iter last, string cont_kind)  
{  
    cout << "Check: " << cont_kind << " is ";  
    if (!is_sorted(first, last)) cout << "not ";  
    cout << "sorted\n";  
}

Answer 1

main应该如何了解s，l和v？它们是完全不相关的函数的局部变量（insert_xxx个），main无法知道它们。如果你想让它们全局可访问，只需将它们设为全局变量，即将它们的定义放在main之前：

// ...

list<double> l;
set<double> s;
vector<double> v;

int main(){
  // ....
}

// ...

Answer 2

看起来l在'insert_list'函数中定义，并且在main中不可用。只有内部函数定义的变量才可用。

Answer 3

您似乎根本没有声明变量。为什么你认为它们应该存在于主体？在我能看到的任何地方都没有全局或本地人。在使用它们之前尝试声明它们。

在此范围内未声明的变量

3 个答案: