Question

因此，此代码的任务是复制学生＆＃39;从csv excel表到xcode的名称和等级，然后将它们放入数组并将它们放入新的Excel工作表中。我似乎遇到的问题是getline没有进入下一行。为了确保在这段代码中某处不会出现导致这种情况发生的错误，我编写了一个非常小且完全不同的程序来查看getline是如何工作的，并发现它不会跳到下一行。事实上，如果我将字符数量提高到一个很高的数字，它只会将整个excel信息复制到数组中。这是我的代码：

#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();
}

这是我用来测试以查看getline是否实际移动到下一行的代码。

#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

从文件中读取的通常习惯是使用while语句。

在您的情况下，您可以使用另一个变量限制它：

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;
}

如果文件操作失败或已达到最大记录，则输入会话将终止。

getline重复相同的行（c ++）（xcode）

1 个答案: