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C中的fscanf csv未分配值

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我试图创建一个文件来读取包含CSV的文本文件 . 但是出于某种原因,一些Fscanfs不会返回值,但有些值会返回 .

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,但所有其他值都没有返回值 . 我看不到任何东西,它们看起来都是一样的同样的格式文件格式是这样的:

你用什么函数打开文件?,fscanf,fclose,fopen,main,3

以下哪一项不是变量类型?,int,float,char,string,4

3 回答

  • 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 ','
    
  • 0
    • 需要使用足够大小的缓冲区 . 答案,作为一个字符串需要至少2 char . @Daniel

    • fscanf() 应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 ',' ,请不要使用 "%[^,]" 作为最后一个值,否则 fscanf() 将读取下一行 .

    • 建议使用空格来引导每个 "[^,]" 以跳过前导空白区域 .

    if (fscanf(reader, " %50[^,], %29[^,], %29[^,], %29[^,], %29[^,],%1s",
    
    • 更好:用 fgets() 读取行,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();
    }
    
  • 0

    answer 的缓冲区太小,所以 fscanf 写得太多导致损坏 .

    你给它的大小只有一个字符,但 fscanf 会写入两个字符:你想要的字符,3和空字符 \0 .

    将缓冲区大小增加到2可以解决问题 .

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