函數getline重複同一線（C++）（xcode中）

Question

所以對於這個代碼的任務是學生的姓名和等級從CSV複製Excel表單到xcode中，然後把它們放進陣列和把它們放入一個新的Excel表。我似乎遇到的問題是getline不會進入下一行。爲了確保有這個代碼，會導致這樣的事情發生的地方是不是一個錯誤，我寫了一個非常小的，完全不同的程序，看看如何函數getline工作，發現它並沒有跳到下一行。事實上，如果我將字符數量提高到一個很高的數字，它只會將整個Excel信息複製到數組中。這裏是我的代碼：

#include <iostream> 
#include <fstream> 
#include <cstring> 
#include <cstdlib> 



using namespace std; 

char line[80]; 
string students[100]; 
int grades[50][20]; 
char *p; 
int r; 
int q; 


void read_sheet(); 
void print_sheet(); 

int main() { 

read_sheet(); 

print_sheet(); 

return 0; 
} 

void read_sheet(){ 

ifstream file1("/Users/JohnnyD/Downloads/Project_MAC101.csv"); 


file1.getline(line, 79); // this puts everything from the first line of the 
         // excel sheet into the array line 


for(r=0;r<50||(!file1.eof());r++){ // this is a loop that goes up to 
            // either the amount of students 
            //(50 is max) or the end of the 

    file1.getline(line, 79); // this is suppose to put everything 
           //from the second line into the array 
           // line, but I don't think it is doing 
           // that. 

    p=strtok(line,",");   // this takes everything from the first 
           // line that is before the comma and 
           //puts it into p.(should be only a single 
           // student's name 
    students[r]=p;    // this puts the name into the array 
           // called students 

    cout << students<<endl; // this is only a test to see if the names 
           // are going properly to the array. I 
           // wouldn't normally have this in the code. 
           // This is where I found out that it's not 
           // skipping to the next line because the 
           // output just spits out "name" over and 
           // over again which means that it never got 
           // passed the first word in the excel sheet. 
           // ("name" is the first word in the first 
           // line in the excel sheet) 

    for(q=0;q<20;q++){   // this is a loop that goes to the end of 
           // the column where 20 is the max amount 
           // of grades 

     p=strtok(NULL,",");  // puts each grade before the comma into p. 
     if(p==NULL)    // if it's the end of the line, break out 
      break;      //of the loop. 

     grades[r][q]=atoi(p); // this changes the string to integer and then 
           // puts it into the array grades 


    } 

} 


file1.close(); 
} 



void print_sheet(){ 

ofstream file2("testing.csv"); 

for(int y=0;y<=r;y++){ 

    file2<<students[y]; 
    for(int h=0;h<q;h++){ 

     file2<<grades[y][h]; 
    } 
    file2<<endl; 
} 

file2.close(); 
} 

這是我用來測試的代碼，看看getline是否真的移動到下一行。

#include <iostream> 
#include <fstream> 
#include <cstring> 
#include <cstdlib> 
using namespace std; 
char line[80]; 

int main() { 

ifstream file1("/Users/JohnnyD/Downloads/Project_MAC101.csv"); 

file1.getline(line, 79); 
cout << line<<endl; 

file1.getline(line, 79); // shouldn't this then go to the next line? 
cout << line<<endl;  // It doesn't. It only repeats the first getline 

return 0; 
} 

Answer 1

常用的成語從文件中讀取數據是使用while聲明。

在你的情況，你可以用另一個變量限制它：

const unsigned int maximum_records = 50U; 
unsigned int record_count = 0U; 
std::string text_line; 
// ... 
while (getline(datafile, text_line) && (record_count < maximum_records)) 
{ 
    //... 
    ++record_count; 
} 

如果任何文件操作失敗或最大記錄已經達到，輸入會話將被終止。