如果我没有流但有文件描述符，如何使用 fgets 或 getline？
根据fgets
的联机帮助页不建议混合调用 stdio 的输入函数 对文件描述符的 read(2) 进行低级调用的库 与输入流关联；结果将是不确定的并且 很可能不是你想要的。
您可以使用 read() 函数从文件描述符中读取，这在手册页中非常清楚：
read(int fd, void *buf, size_t count); read() 尝试读取最多 从文件描述符 fd 到从 buf 开始的缓冲区中计数字节。
#include <iostream>
#include <string>
#include <fstream>
#include <iomanip>
#include <limits>
#include <algorithm>
using namespace std;
const int MAX_TOPPINGS = 2;
const int MAX_DONUTS = 50;
struct donutType {
string name;
bool type;
double price;
string filling;
string toppings[MAX_TOPPINGS];
};
ifstream getFileStream(string);
int getDonuts(ifstream&, donutType[]);
bool continueMenu(string);
void sortByPrice(donutType[], int);
int searchByName(const donutType[], int, string);
void removeDonutFromList(donutType[], int&, int);
int getCheapestDonut(const donutType[], int);
void soldDonut(donutType, donutType[], int&);
void outputSoldDonuts(ofstream&, const donutType[], int);
void displayAvailableDonuts(const donutType[], int);
string allCaps(string);
/**
* The main function to manage the donut ordering program.
*
* @return The exit status of the program.
*/
int main() {
ifstream infile;
ofstream outfile("sold.csv");
string filename;
string request;
donutType donuts[MAX_DONUTS];
donutType soldDonuts[MAX_DONUTS];
int amtDonuts = 0;
int amtSold = 0;
double total = 0;
cout << fixed << setprecision(2);
// gets step 1 the input stream
infile = getFileStream("Enter a donut file: ");
// step 2 get total donuts
amtDonuts = getDonuts(infile, donuts);
// step 3 print to console
cout << "Welcome to Hank's Donut World!\n\n";
while (true) {
// step 4 print the available donuts to console
displayAvailableDonuts(donuts, amtDonuts);
//step 5 ask for user input
string nameEnteredByUser;
cout << "Enter donut name or cheapest: ";
getline(cin, nameEnteredByUser);
// step 6 check the user input choice and call function accordingly
int donutIndex;
transform(nameEnteredByUser.begin(), nameEnteredByUser.end(),
nameEnteredByUser.begin(), ::tolower);
if (nameEnteredByUser.compare("cheapest") == 0)
donutIndex = getCheapestDonut(donuts, amtDonuts);
else
donutIndex = searchByName(donuts, amtDonuts, nameEnteredByUser);
// step 7 check if the search results was empty
if (donutIndex == -1) {
cout << "Donut not found!\n";
continue;
}
// step 8 print the selection to console
cout << "You selected " << donuts[donutIndex].name
<< ".\nExcellent choice!\n";
// Step 9 inserting the sold donut into solddonuts array
total += donuts[donutIndex].price;
soldDonuts[amtSold] = donuts[donutIndex];
amtSold++;
// Step 10 removing the donut from donuts array
removeDonutFromList(donuts, amtDonuts, donutIndex);
// Step 11 choice to continue with more purchase
bool complete = continueMenu("Will this complete your order? ");
if (!complete) {
if (amtDonuts > 0)
continue; // go to Step 4
else
break; // End the program if there are no available donuts left
}
// Step 13 sort the donuts sold by price using bubble sort
sortByPrice(soldDonuts, amtSold);
// Step 14
if (outfile.is_open()) {
outfile << "Sold," << fixed << setprecision(2) << total << "\n";
outputSoldDonuts(outfile, soldDonuts, amtSold);
} else {
cerr << "Error opening output file.\n";
}
break; // End the program
}
return 0;
}
/**
* Retrieves an input file stream for a given filename after prompting the user.
*
* @param msg The message to prompt the user for the filename.
* @return An ifstream object for the specified filename.
*/
ifstream getFileStream(string msg) {
ifstream fileStream;
string fileName;
while (true) {
// Prompt user for a filename
cout << msg;
getline(cin, fileName);
// Open the file stream
fileStream.open(fileName);
// Check if the file stream is open
if (fileStream.is_open()) {
break;
} else {
fileStream.clear(); // Clear any error flags
cin.ignore(numeric_limits<streamsize>::max(), '\n'); // Clear input buffer
}
}
return fileStream;
}
/**
* Reads donut data from an input file stream into a struct array of donutType.
*
* @param infile An input file stream containing donut data.
* @param donuts An array of donutType to store the read data.
* @return The number of donuts read from the file.
*/
int getDonuts(ifstream &infile, donutType donuts[]) {
const int MAX_RECORDS = 50;
size_t MAX_CHARS = 100;
char line[MAX_CHARS];
int count = 0;
// Read and ignore the header line
infile.getline(line, MAX_CHARS);
// Read the CSV file line by line
while (!infile.fail() && count < MAX_RECORDS) {
// Read the entire line into 'line'
infile.getline(line, MAX_CHARS);
// Create a strings to parse the line
string lineString(line);
if(lineString.size() < 2)
break;
// Tokenize the line based on commas
size_t start = 0;
size_t end = lineString.find(',');
// Read name
donuts[count].name = lineString.substr(0, end);
//add plus one to skip the comma
lineString = lineString.substr(end+1);
// Read type
end = lineString.find(',');
donuts[count].type = (lineString.substr(0, end) == "Cake");
lineString = lineString.substr(end+1);
// Read filling
end = lineString.find(',');
donuts[count].filling = lineString.substr(0, end);
lineString = lineString.substr(end+1);
// Read toppings
end = lineString.find(',');
donuts[count].toppings[0] = lineString.substr(0, end);
lineString = lineString.substr(end+1);
end = lineString.find(',') ;
donuts[count].toppings[1] = lineString.substr(0, end);
lineString = lineString.substr(end+1);
// Read price
donuts[count].price = stod(lineString);
count++;
}
return count;
}
/**
* Displays a prompt and waits for user input to continue or exit.
*
* @param prompt The message to display as a prompt.
* @return True if the user chooses to continue, false if the user chooses to exit.
*/
bool continueMenu(string prompt) {
string input;
while (true) {
cout << prompt;
getline(cin, input);
// Convert the input to lowercase for case-insensitive comparison
transform(input.begin(), input.end(), input.begin(), ::tolower);
if (input == "no")
return false;
else if (input == "yes")
return true;
else
cerr << "Invalid input. Please enter 'Yes' or 'No' (case insensitive).\n";
}
}
/**
* Sorts an array of donuts based on their prices in ascending order using bubble sort.
*
* @param donuts An array of donuts to be sorted.
* @param amtDonuts The number of donuts in the array.
*/
void sortByPrice(donutType donuts[], int amtDonuts) {
for (int i = 0; i < amtDonuts - 1; ++i) {
for (int j = 0; j < amtDonuts - i - 1; ++j) {
// Compare prices and swap if needed
if (donuts[j].price > donuts[j + 1].price) {
// Swap
donutType temp = donuts[j];
donuts[j] = donuts[j + 1];
donuts[j + 1] = temp;
}
}
}
}
/**
* Searches for a donut by name in an array of donuts.
*
* @param donuts An array of donuts to be searched.
* @param amtDonuts The number of donuts in the array.
* @param name The name of the donut to be searched.
* @return The index of the found donut if present, otherwise -1.
*/
int searchByName(const donutType donuts[], int amtDonuts, string name) {
transform(name.begin(), name.end(), name.begin(), ::tolower);
for (int i = 0; i < amtDonuts; ++i) {
string donutName = donuts[i].name;
transform(donutName.begin(), donutName.end(), donutName.begin(),
::tolower);
if (donutName.compare(name) == 0)
return i; // Return the index if the name is found
}
return -1; // Return -1 if the name is not found
}
/**
* Finds the index of the cheapest donut in an array of donuts.
*
* @param donuts An array of donuts to be searched.
* @param amtDonuts The number of donuts in the array.
* @return The index of the cheapest donut if the array is not empty, otherwise -1.
*/
int getCheapestDonut(const donutType donuts[], int amtDonuts) {
if (amtDonuts <= 0)
return -1; // Return -1 if the array is empty
// Initialize to maximum possible value
double minPrice = donuts[0].price;
// Index of the cheapest donut
int minIndex = 0;
for (int i = 1; i < amtDonuts; ++i) {
if (donuts[i].price < minPrice) {
minPrice = donuts[i].price;
minIndex = i;
}
}
return minIndex;
}
/**
* Converts a given string to uppercase.
*
* @param s The input string to be converted to uppercase.
* @return The uppercase version of the input string.
*/
string allCaps(string s) {
string upper = s;
for (char &c : upper)
c = toupper(static_cast<unsigned char>(c));
return upper;
}
/**
* Removes a donut from the list based on the provided index.
*
* @param donuts The array of donuts.
* @param amtDonuts The current number of donuts in the array.
* @param removeIndex The index of the donut to be removed.
*/
void removeDonutFromList(donutType donuts[], int &amtDonuts, int removeIndex) {
if (removeIndex < 0 || removeIndex >= amtDonuts) {
cerr << "Invalid index to remove. Index out of range." << endl;
return;
}
// Shift elements to fill the gap
for (int i = removeIndex; i < amtDonuts - 1; ++i) {
donuts[i] = donuts[i + 1];
}
// Decrement the amount of donuts
amtDonuts--;
}
/**
* Outputs information about sold donuts to an output file.
*
* @param outfile The output file stream.
* @param soldDonuts The array of sold donuts.
* @param amtSold The current number of sold donuts in the array.
*/
void outputSoldDonuts(ofstream &outfile, const donutType soldDonuts[],
int amtSold) {
if (!outfile.is_open()) {
cerr << "Error: Output file is not open." << endl;
return;
}
outfile << fixed << setprecision(2);
outfile << "Name,Type,Filling,Topping1,Topping2,Price" << endl;
for (int i = 0; i < amtSold; ++i) {
outfile << soldDonuts[i].name << ",";
outfile << (soldDonuts[i].type ? "Cake" : "Dough") << ",";
outfile << soldDonuts[i].filling << ",";
outfile << soldDonuts[i].toppings[0] << ",";
outfile << soldDonuts[i].toppings[1] << ",";
outfile << soldDonuts[i].price << "\n";
}
}
/**
* Displays the list of available donuts with their names and prices.
*
* @param donuts The array of available donuts.
* @param amtDonuts The current number of available donuts in the array.
*/
void displayAvailableDonuts(const donutType donuts[], int amtDonuts) {
cout << "List of donuts" << endl;
cout << "---------------------------" << endl;
int count = 0;
for (int i = 0; i < amtDonuts; ++i)
cout << donuts[i].name << " " << donuts[i].price << endl;
cout << endl;
}