fscanf csv in C.未分配的值

Question

我试图创建一个文件来读取包含CSV的文本文件。然而，出于某种原因，一些fscanf不返回值，但有些返回值。

FILE* reader;
char OptionOne[30]="";
char OptionTwo[30]="";
char OptionThree[30]="";
char OptionFour[30]="";
char answer[1]="";
char CorrectAnswer[1];
char Question[51];

reader = fopen("C:\\Users\\Finley\\Desktop\\Programming\\QuizMachine\\QuizMachine\\fscanf_questions.txt", "r");

if (reader == NULL)
{
    printf("Unable to Open File: %s\n", FileName);
}

fscanf(reader, "%[^,],", Question);
fscanf(reader, "%[^,],", OptionOne);
fscanf(reader, "%[^,],", OptionTwo);
fscanf(reader, "%[^,],", OptionThree);
fscanf(reader, "%[^,],", OptionFour);
fscanf(reader, "%[^,],", answer);

为什么第一个fscanf返回一个值，而其他所有fscanf都不返回一个值。我什么也看不见，它们看起来都一样，格式相同。文件格式如下：

您使用什么功能打开文件？，fscanf、fclose、fopen、main、3

以下哪项不是变量类型？，int，float，char，string，4

Answer 1

this line: fscanf(reader, "%[^,],", Question); (and those like it) 
have a couple of problems. 
1) should always check the returned value from a input I/O statement
   to assure the conversion was successful 
2) the format string is missing the type conversion, in this case 's'
this line: fscanf(reader, "%[^,],", answer); will fail if the line does not end in a ','


"Why does the first fscanf return a value but all the others not return a value." 
ans: 1) because the ' ' after the comma is not consumed
     2) use a leading ' ' in the format strings to consume white space
        this will also consume an trailing '\n' on each line
     3) a type specifier is NOT optional in a format string, use 's'
     3a) I would have read in the 'answer' as a char using '%c' for a format conversion
         and only created a char, not a char array.
     4) to avoid buffer overruns, 
        include the 'size-1' optional part of each format  conversion,
        just in case some string length is = or greater than the 
        receiving buffer

"I cannot see anything and they all seem the same with the same formating
File formatting is like this:"
ans: where is the file formatting info?

this line: printf("Unable to Open File: %s\n", FileName); 
the variable FileName is not set. 
suggest setting char * FileName = C:\\Users\\Finley\\Desktop\\Programming\\QuizMachine\\QuizMachine\\fscanf_questions.txt‌​" 
and using 'FileName' in the fopen() statement. 

this line: printf("Unable to Open File: %s\n", FileName); 
after this line, should insert 'exit(EXIT_FAILURE);
rather than continue in the program, trying to use that NULL file descriptor pointer 

this line: char answer[1]=""; 
will be a problem as the input is being read in as strings, 
so even for a single char string, there still needs to be
room for the trailing '\0'

this line: fscanf(reader, "%[^,],", answer);
1) fails if each line of the input file, including the last line,
   does not end in ','

Answer 2

回答的缓冲区太小，所以fscanf写入太多，导致损坏。

您给它的大小只有一个字符，但是fscanf将在其中写入两个字符：您想要的字符3和空字符\0。

将缓冲区大小增加到2可以解决此问题。

Answer 3

>

需要使用足够大小的缓冲区。答案，因为一个字符串至少需要2char.@Daniel

fscanf（）应该限制输入以防止缓冲区损坏。宽度说明符通常比缓冲区的大小小1。

char Question[51];   
fscanf(reader, "%50[^,],", Question);

应该检查fscanf（）的结果。

if (fscanf(reader, "%50[^,],%29[^,],%29[^,],%29[^,],%29[^,],%1s", 
    Question, OptionOne, OptionTwo, OptionThree, OptionFour, answer) != 6) {
  Handle_Bad_input();
}

如果输入没有以下，“”，则不要对最后一个值使用“%[^，]”，否则fscanf（）将读取下一行。

建议在每个“[^，]”前面加一个空格，以跳过前面的空白。

if (fscanf(reader, " %50[^,], %29[^,], %29[^,], %29[^,], %29[^,],%1s", 

更好的是：使用fget（）读取该行，然后扫描缓冲区。

char buf[200];
if (fgets(buf, sizeof buf, reader) == NULL) Handle_IOErrorOrEOF();
if (sscanf(buffer, "%50[^,],%29[^,],%29[^,],%29[^,],%29[^,],%1s", 
    Question, OptionOne, OptionTwo, OptionThree, OptionFour, answer) != 6) {
  Handle_Bad_input();
}