[英]C++ write file error
我的文字檔:
1:Meat Dish:Steak:11.5
2:Fish Dish:Fish and chips:12
所以基本上我想讀取文件,選擇1或2選擇一個菜,然后將名稱和價格寫入文件。
這是我的代碼:
#include <iostream>
#include <fstream>
#include <string>
#include <vector> // We will use this to store Players
using std::string;
using std::ofstream;
using std::ifstream;
using std::cout;
using std::cin;
using std::vector;
struct MenuList { // Define a "Menuu" data structure
string itemNo;
string category;
string descript;
double price;
};
std::istream& operator>>(std::istream& infile, MenuList& menu) {
getline(infile, menu.itemNo, ':');
getline(infile, menu.category, ':');
getline(infile, menu.descript, ':');
infile >> menu.price;
// When we have extracted all of our information, return the stream
return infile;
}
std::ostream& operator<<(std::ostream& os, MenuList& menu) {
os << "" << menu.itemNo << " " << menu.category << " - " <<
menu.descript;
// When we have extracted all of our information, return the stream
return os;
}
void Load(vector<MenuList>& r, string filename) {
std::ifstream ifs(filename.c_str()); // Open the file name
if(ifs) {
while(ifs.good()) { // While contents are left to be extracted
MenuList temp;
ifs >> temp; // Extract record into a temp object
r.push_back(temp); // Copy it to the record database
}
cout << "Read " << r.size() << " records.\n\n";
}
else {
cout << "Could not open file.\n\n";
}
}
void Read(vector<MenuList>& r) {// Read record contents
for(unsigned int i = 0; i < r.size(); i++)
cout << r[i] << "\n";
}
void Search(vector<MenuList>& r) {// Search records for itemNo
string n;
int a;
char cont;
cout << "Order\n_______\n";
do {
cout << "Enter quantity: ";
cin >> a;
cout << "Enter dish: ";
cin >> n;
for(int i = 0; i < r.size(); i++) {
if(r[i].itemNo.find(n) != string::npos)
cout << r[i].category << " - " <<r[i].descript << ' ' <<
a*r[i].price;
std::ofstream ofs;
ofs.open ("transactions.txt", std::ofstream::out | std::ofstream::app);
ofs << r[i].category << " - " <<r[i].descript << ' ' << a*r[i].price << "\n";
}
cout << "\n\nContinue to add to order?(y)";
cin >> cont;
}while(cont == 'y');
}
int main() {
vector<MenuList> records;
Load(records, "delete.txt");
Read(records);
Search(records);
return 0;
}
當我輸入要在屏幕上顯示的菜式並寫入文件時,在屏幕上顯示菜式就可以了,但是當它將菜式寫入文件時,即使我只選擇了一個菜,也將它們都寫入了。
如果選擇第一道菜,則預期輸出到文件中:
Meat Dish - Steak 11.5
但是我得到的是:
1:Meat Dish:Steak:11.5
2:Fish Dish:Fish and chips:12
問題在這里附近:
do {
cout << "Enter quantity: ";
cin >> a;
cout << "Enter dish: ";
cin >> n;
for(int i = 0; i < r.size(); i++) {
if(r[i].itemNo.find(n) != string::npos)
cout << r[i].category << " - " <<r[i].descript << ' ' <<
a*r[i].price;
std::ofstream ofs;
ofs.open ("transactions.txt", std::ofstream::out | std::ofstream::app);
ofs << r[i].category << " - " <<r[i].descript << ' ' << a*r[i].price << "\n";
}
cout << "\n\nContinue to add to order?(y)";
cin >> cont;
}while(cont == 'y');
在這一點上的任何幫助。 先感謝您。
您對該文件的實際輸出顯然來自您定義的重載<<運算符:
std::ostream& operator<<(std::ostream& os, MenuList& menu) {
在您的第一個代碼段中,因為它以數字開頭。
我完全不清楚這行代碼是什么
ofs << r[i].category << " - " <<r[i].descript << ' ' << a*r[i].price << "\n";
確實給出了一個事實,即<<操作符僅將流和引用作為參數。 我以為您會遇到編譯錯誤。 相反,我猜測<<函數被多次調用。
我建議您擺脫重載的<<和>>,而只需使用系統標准的字母進行讀和寫。
或者,也許可以使用重載運算符,但是將期望的對象傳遞給它。
不帶括號的if語句只會影響以下代碼行。 因此,只有以下一行受該條件的影響。
if(r[i].itemNo.find(n) != string::npos)
cout << r[i].category << " - " <<r[i].descript << ' ' << a*r[i].price;
為了只將滿足條件的條目寫入文件,可以如下添加大括號:
for(int i = 0; i < r.size(); i++) {
if(r[i].itemNo.find(n) != string::npos){
cout << r[i].category << " - " <<r[i].descript << ' ' << a*r[i].price;
std::ofstream ofs;
ofs.open ("transactions.txt", std::ofstream::out | std::ofstream::app);
ofs << r[i].category << " - " <<r[i].descript << ' ' << a*r[i].price << "\n";
}
}
這將包括條件中的所有代碼。
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