我在以下函数中出现了“未在此范围内声明”的错误：
double monteCarlo(void)
{
double intervalArea = 2*(upperBound - lowerBound); // (f_max(x)) - f_min(x))*(upperBound - lowerBound) - Could be calculated from derivative, but known for this function.
for (uint currentPoints = (numPoints/100); currentPoints < numPoints; currentPoints += (numPoints/100))
{
double area = randx = randy = 0;
uint underCurve = 0;
gsl_rng* rndGen = gsl_rng_alloc (gsl_rng_mt19937); // Initialize random number generation
gsl_rng_set(rndGen,timeSeed()); // Seed random number generation
for (uint point= 1; point <= currentPoints; point++)
{
randx = gsl_rng_uniform(rndGen); randy = ((2*gsl_rng_uniform_pos(rndGen)) -1);
if (randy <= f(ranx))
{
underCurve++;
}
}
area = (underCurve/currentPoints)*intervalArea;
output << currentSubintervals << "\t" << area << std::endl;
}
return area;
}
double trapezoidal(void)
{
for (uint currentSubintervals = 1; currentSubintervals <= subintervals; currrentSubintervals++)
{
double area = stepSize = sum = 0;
double stepSize = ((upperBound - lowerBound)/currentSubintervals);
double sum = (f(lowerBound) + f(upperBound))/2;
for (uint currentInterval = 1; i < currentSubintervals; currentInterval++)
{
sum += f(lowerBound + (currentInterval*stepSize));
}
area = stepSize*sum;
output << currentSubintervals << "\t" << area << std::endl;
}
return area;
}
我得到的错误是：
g++ -c -Wall -std=c++11 integrate.cpp -o integrate.o
integrate.cpp: In function ‘double monteCarlo()’:
integrate.cpp:118:17: error: ‘randx’ was not declared in this scope
integrate.cpp:118:25: error: ‘randy’ was not declared in this scope
integrate.cpp:126:19: error: ‘ranx’ was not declared in this scope
integrate.cpp:133:13: error: ‘currentSubintervals’ was not declared in this scope
integrate.cpp:136:9: error: ‘area’ was not declared in this scope
integrate.cpp: In function ‘double trapezoidal()’:
integrate.cpp:141:74: error: ‘currrentSubintervals’ was not declared in this scope
integrate.cpp:143:17: error: ‘stepSize’ was not declared in this scope
integrate.cpp:143:28: error: ‘sum’ was not declared in this scope
integrate.cpp:148:34: error: ‘i’ was not declared in this scope
integrate.cpp:156:9: error: ‘area’ was not declared in this scope
integrate.cpp:157:1: warning: control reaches end of non-void function [-Wreturn-type]
integrate.cpp: In function ‘double monteCarlo()’:
integrate.cpp:137:1: warning: control reaches end of non-void function [-Wreturn-type]
make: *** [integrate.o] Error 1
这是......非常奇怪，因为变量都是在函数本身中声明和使用的。我试图在MWE中重现它，但我什么都没有。
我能真正问的是......帮助吗？我不知道这里有什么问题。我已经尝试了几个小时，并且搜索了很多。
#include "integrate.hpp"
//=======================
// Globals
static uint algorithm_flag = 0; // Flag for which algoirthm to use
static std::string algorithm = "none";
static double lowerBound = 0, upperBound = 1; // "Global" bounds for algorithms
static uint subintervals = 0, numPoints = pow(2,16);
static int option_index = 0;
static std::ofstream output ("integrate.data");
//=======================
// Main
int main(int argc, char **argv)
{
std::cout << " Numerical Integrator of cos(1/x)!\n"
<< "-----------------------------------\n";
if (!(handleArgs(argc, argv)))
{
throw std::invalid_argument(argv[option_index]);
return -1;
}
std::cout << " Algorithm: " << algorithm << std::endl
<< " Lower Bound: " << lowerBound << std::endl
<< " Upper Bound: " << upperBound << std::endl;
switch(algorithm_flag)
{
case 1:
std::cout << " Number of Points: " << numPoints << std::endl << " Number of Subintervals: " << subintervals;
break;
case 2:
std::cout << " Number of Points: " << numPoints;
break;
case 3:
std::cout << " Number of Subintervals: " << subintervals;
break;
}
std::cout << std::endl << "-----------------------------------" << std::endl;
double area, diff, percentError, actualArea = -0.08441095055957388688903177037359518055393632433151889234592026720612077182783481670736342350213473343;
if (algorithm_flag == 2 || algorithm_flag == 1)
{
std::cout << " Monte Carlo:" << std::endl;
area = monteCarlo();
diff = area - actualArea;
percentError = (diff/actualArea)*100;
std::cout << " Calculated area:\t" << area << std::endl
<< " Error:\t\t\t" << diff << std::endl
<< " Accuracy:\t\t" << percentError << "%" << std::endl;
}
else if (algorithm_flag == 3 || algorithm_flag == 1)
{
std::cout << " Trapezoid: " << std::endl;
area = trapezoidal();
diff = area - actualArea;
percentError = (diff/actualArea)*100;
std::cout << " Calculated area:\t" << area << std::endl
<< " Error:\t\t\t" << diff << std::endl
<< " Accuracy:\t\t" << percentError << "%" << std::endl;
}
else
{
std::cout << " Please specify a numerical integration algorithm!" << std::endl
<< "\tSpecify the -m flag for Monte Carlo" << std::endl
<< "\tSpecify the -t flag for Trapezoial" << std::endl
<< "\tSpecify the -a flag for both algorithms" << std::endl;
throw std::logic_error(algorithm);
return -2;
}
std::cout << std::endl << "-----------------------------------" << std::endl
<< "Please see ./integrate.data for the full details of the integration." << std::endl;
output.close();
return 0;
}
//=======================
// Functions
double f(double x)
{
double y = cos(1/x);
return y;
}
double monteCarlo(void)
{
double intervalArea = 2*(upperBound - lowerBound); // (f_max(x)) - f_min(x))*(upperBound - lowerBound) - Could be calculated from derivative, but known for this function.
for (uint currentPoints = (numPoints/100); currentPoints < numPoints; currentPoints += (numPoints/100))
{
double area = randx = randy = 0;
uint underCurve = 0;
gsl_rng* rndGen = gsl_rng_alloc (gsl_rng_mt19937); // Initialize random number generation
gsl_rng_set(rndGen,timeSeed()); // Seed random number generation
for (uint point= 1; point <= currentPoints; point++)
{
randx = gsl_rng_uniform(rndGen); randy = ((2*gsl_rng_uniform_pos(rndGen)) -1);
if (randy <= f(ranx))
{
underCurve++;
}
}
area = (underCurve/currentPoints)*intervalArea;
output << currentSubintervals << "\t" << area << std::endl;
}
return area;
}
double trapezoidal(void)
{
for (uint currentSubintervals = 1; currentSubintervals <= subintervals; currrentSubintervals++)
{
double area = stepSize = sum = 0;
double stepSize = ((upperBound - lowerBound)/currentSubintervals);
double sum = (f(lowerBound) + f(upperBound))/2;
for (uint currentInterval = 1; i < currentSubintervals; currentInterval++)
{
sum += f(lowerBound + (currentInterval*stepSize));
}
area = stepSize*sum;
output << currentSubintervals << "\t" << area << std::endl;
}
return area;
}
bool handleArgs(int argc, char *argv[])
{
int arg = 0;
bool rtVal = true;
while ((arg = getopt_long (argc, argv, "mtau:l:i:p:",long_options, &option_index)) != -1)
{
if(optarg == 0)
{
continue;
}
switch(arg)
{
case 'a':
if (algorithm_flag > 1)
{
std::cout << "Cannot specify more than one algoirthm type, please use --all for both, or use only one";
}
algorithm_flag = 1;
algorithm = "Monte Carlo and Trapezoidal";
break;
case 'm':
if (algorithm_flag)
{
std::cout << "Cannot specify more than one algoirthm type, please use --all for both, or use only one";
}
algorithm_flag = 2;
algorithm = "Monte Carlo";
break;
case 't':
if (algorithm_flag)
{
std::cout << "Cannot specify more than one algoirthm type, please use --all for both, or use only one";
}
algorithm_flag = 3;
algorithm = "Trapezoidal";
break;
case 'u':
upperBound = atoi(optarg);
break;
case 'l':
lowerBound = atoi(optarg);
break;
case 'i':
subintervals = atoi(optarg);
break;
case 'p':
numPoints = atoi(optarg);
break;
case '?':
/* getopt already printed an error message. */
rtVal = false;
break;
default:
rtVal = false;
}
if(!(rtVal))
{
std::cout << "Invalid option " << arg;
if (optarg)
{
std::cout << " with arg " << optarg;
}
std::cout << std::endl;
throw std::invalid_argument(argv[option_index]);
break;
}
}
return rtVal;
}
头文件是：
//=======================
// Guard Statment
#ifndef __SAWHPP_INCLUDED__
#define __SAWHPP_INCLUDED__
//=======================
// Dependencies
#include <iostream>
#include <vector>
#include <string>
#include <cmath> // Math Functions Used
#include <ctime> // Random Number Seed
#include <stdexcept>
#include <fstream>
#include <cstdlib>
#include <getopt.h>
#include <gsl/gsl_rng.h> // Random Number Generation
//=======================
// Prototypes
bool handleArgs(int argc, char *argv[]);
double monteCarlo(void);
double trapezoidal(void);
double f(double x);
//=======================
// Objects and Datatypes
typedef unsigned long int ulong;
typedef unsigned int uint;
static struct option long_options[] =
{
{"montecarlo", no_argument, 0, 'm'},
{"trapezoidal", no_argument, 0, 't'},
{"all" , no_argument, 0, 'a'},
{"upper", optional_argument, 0, 'u'},
{"lower", optional_argument, 0, 'l'},
{"subintervals", optional_argument, 0, 'i'},
{"points", optional_argument, 0, 'p'},
{nullptr, 0, 0, 0}
};
//=======================
// Trivial Functions
unsigned long int timeSeed()
{
std::time_t rawtime;
std::tm* currentTime;
std::string timeString;
std::time(&rawtime); // Seconds since 00:00:00 UTC, January 1, 1970
currentTime = std::gmtime(&rawtime); // Convert to GMT
std::strftime(&timeString[0],timeString.max_size(),"%Y%m%d%H%M%S",currentTime); // Convert to String
return std::strtol(timeString.c_str(),nullptr,10); // Convert to int.
}
#endif // Guard Statment
答案 0 :(得分：5)
double area = stepSize = sum = 0;只是area的声明，并且已经声明stepSize和sum。他们不是。
将其更改为
double area, stepSize, sum;
area = stepSize = sum = 0;
另外
currrentSubintervals
和
currentSubintervals
是两件不同的事情。对此，我只能说 - WTH兄弟？
答案 1 :(得分：0)
double area = randx = randy = 0;
可以预测，您希望声明三个变量。它没有;它只是声明area，randx = randy = 0作为初始化。你需要三个独立的声明符：
double area=0, randx=0, randy=0;
或三个单独的声明声明。
答案 2 :(得分：0)
double area = randx = randy = 0;
那是什么意思？它说“定义一个类型的变量，名为area，并使用已存在的变量randx的值对其进行初始化，这将是被分配另一个已存在的变量randy的值，该变量将被赋值为0.“
编译器不知道名称为randx和randy的任何现有变量。
我猜你真正想要的是定义三个新变量，所有这些变量都用0初始化。你可以像这样在单行中完成：
double area=0, randx=0, randy=0;
或者只是逐个定义：
double area=0;
double randx = 0;
double randy = 0;
这可能会有点打字但提高了可读性，而且人们通常会阅读程序而不是书面编写程序，因此保存一些关键笔划是不值得的。
更好的方法是在需要时定义变量，而不是更早。
然后有第二个错误：你返回一个area - 但是你只在for循环中定义了那个变量，所以当你调用return时它不存在。
double monteCarlo(void)
{
const double intervalArea = 2*(upperBound - lowerBound);
for (uint currentPoints = (numPoints/100); currentPoints < numPoints; currentPoints += (numPoints/100))
{
gsl_rng* rndGen = gsl_rng_alloc (gsl_rng_mt19937); // Initialize random number generation
gsl_rng_set(rndGen,timeSeed()); // Seed random number generation
uint underCurve = 0;
for (uint point= 1; point <= currentPoints; point++)
{
double randx = gsl_rng_uniform(rndGen);
double randy = ((2*gsl_rng_uniform_pos(rndGen)) -1);
if (randy <= f(randx))
{
underCurve++;
}
}
double area = (underCurve/currentPoints)*intervalArea;
output << currentSubintervals << "\t" << area << std::endl;
}
return /** ??? **/;
}