有没有处理“错误:使用未声明的标识符‘”的方法？
有没有处理“错误:使用未声明的标识符‘”的方法？
提问于 2022-04-11 21:53:35
我有以下几段代码，并且得到了一堆相同的未声明标识符错误。根据我编写的其他代码，主文件上的#include "rec_fun.h“应该允许在该文件中使用函数。因为我同时编译了rec_fun.cpp和main.cpp，这应该会生成一个可执行名称FINAL。
错误：
MaryMcBeth@unknown88665a207c1a Recursion_Program % g++ -std=c++14 rec_fun.cpp main.cpp -o FINAL
main.cpp:17:12: error: use of undeclared identifier 'fib_recursion'
fib_recursion(i);// Replace with call to your function.
^
main.cpp:18:12: error: use of undeclared identifier 'fib_iterative'
fib_iterative(i);
^
main.cpp:28:6: error: use of undeclared identifier 'triangle'
triangle(cout, 3, 5);
^
main.cpp:31:6: error: use of undeclared identifier 'numbers'
numbers(cout, "THERBLIG", 2);
^
4 errors generated.
MaryMcBeth@unknown88665a207c1a Recursion_Program % main.cpp：
#include <iostream>
#include <chrono>
#include "rec_fun.h"
using namespace std;
using namespace std::chrono;
int main()
{
high_resolution_clock::time_point startTime = high_resolution_clock::now();
int i;
for (i = 0; i < 1000000; i++)
{
fib_recursion(i);// Replace with call to your function.
fib_iterative(i);
}
high_resolution_clock::time_point endTime = high_resolution_clock::now();
duration<float> time_span = endTime - startTime;
std::cout << fixed;
std::cout << "It took " << time_span.count() << " seconds.";
std::cout << std::endl;
cout<<"---------------"<<endl;
triangle(cout, 3, 5);
return 0;
cout<<"------------------"<<endl;
numbers(cout, "THERBLIG", 2);
cout<<"-------------------------"<<endl;
}rec_fun.cpp：
#include<iostream>
#include <chrono>
#include "rec_fun.h"
#include <string>
using namespace savitch2;
using namespace std;
using namespace std::chrono;
void recursion::numbers(ostream &outs, const string& prefix, unsigned int levels)
{
if(levels == 0)
outs << prefix << endl;
else
{
for(char c = '1'; c <= '9'; c++)
{
s = prefix + c + '.';
numbers(outs, s, levels-1);
}
}
}
bool recursion::bears(int n)
{
if (n < 42) return false;
if (n == 42) return true;
if ((n%2) == 0)
if (bears(n/2)) return true;
if (((n%3)==0) || ((n%4)==0))
{
ones = n % 10;
tens = (n % 100)/10;
if ((ones != 0) && (tens != 0) && (bears(n-ones*tens)))
return true;
}
if ((n%5) == 0)
if (bears(n-42)) return true;
return false;
}
//recursive helper method to return a string containing count number of '*'
string recursion::asterisks(int count)
{
//if count is above 0, returning one '*' followed by the value returned
//from recursive call to asterisks passing count-1 as argument
if(count>0){
return "*"+asterisks(count-1);
}
//else, if count is 0 or negative, returning empty string
else{
return "";
}
}
//required method
void recursion::triangle(ostream &outs, unsigned int m, unsigned int n)
{
//proceeding only if m<=n.
//if m>n, recursion stops (base case)
if(m<=n){
//making a string containing m number of asterisks
string ast=asterisks(m);
//printing it to outs
outs<<ast<<endl;
//making a recursive call passing m+1 as new m
triangle(outs,m+1,n);
//printing ast to outs once again
outs<<ast<<endl;
}
}
int recursion::fib_iterative(int n) {
if(n == 1 || n == 2)
return 1;
int A[2][2] = { { 1, 1 },{ 1, 0 } };
int B[2][2] = { { 1, 1 },{ 1, 0 } };
int temp[2][2];
while (n >= 2) {
for (int i = 0; i < 2; i++)
for (int k = 0; k < 2; k++) {
temp[i][k] = 0;
for (int j = 0; j < 2; j++)
temp[i][k] += A[i][j] * B[j][k];
}
for (int i = 0; i < 2; i++)
for (int j = 0; j < 2; j++)
B[i][j] = temp[i][j];
n--;
}
return B[0][1];
}
int recursion::fib_recursion(int n)
{
if (n == 0)
return 0;
else if (n == 1)
return 1;
else
return fib_recursion(n-1) + fib_recursion(n-2);
}rec_fun.h：
#include<iostream>
#include <string>
using namespace std;
namespace savitch2
{
class recursion
{
public:
bool bears(int n);
void triangle(ostream &outs, unsigned int m, unsigned int n);
string asterisks(int count);
void numbers(ostream &outs, const string& prefix, unsigned int levels);
int fib_iterative(int n);
int fib_recursion(int n);
private:
int ones;
int tens;
string s;
};
}预期产出：
It took 8 seconds
...回答 2
Stack Overflow用户
回答已采纳
发布于 2022-04-11 22:45:24
你需要做的
int i;
recursion rec;
for (i = 0; i < 1000000; i++)
{
rec.fib_recursion(i);// Replace with call to your function.
rec.fib_iterative(i);因为您的函数是类方法，所以必须创建类的实例才能使用它们。
Stack Overflow用户
发布于 2022-04-11 22:18:49
您需要创建一个类实例。本质上，程序中的函数不是独立的函数，它们是类的方法(在您的例子中是class=recursion)，因此获得错误：‘使用未声明的标识符’是有意义的。
在文件中创建类递归的实例，通过中的该实例调用这些函数。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/71834694
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