Question

我正在写一个测验程序。程序应该从csv文件中读取问题，答案和正确答案。然后它应该将它们存储在数组中。

 void read(char question[][50], char answer1[10][10], char answer2[10][10], char answer3[10][10], char answer4[10][10], int correctAnswer[10], int *size, char fileName[], int noOfQuestion){
FILE *reader;
int count;
char qBuffer[50];
char ansBuffer1[50];
char ansBuffer2[50];
char ansBuffer3[50];
char ansBuffer4[50];
int iBuffer = 0;
*size = 0;


//open file
reader = fopen(fileName, "r");

//checking file is open or not
if (reader == NULL)
{
    printf("Unable to open file %s", fileName);
}
else
{
    fscanf(reader, "%100[^\t*\?,],%[^,],%[^,],%[^,],%[^,],%d", size);
    for (count = 0; feof(reader) == 0 && count<*size && count<noOfQuestion; count++){
    //Reading file
        fscanf(reader, "%100[^\t*\?,],%[^,],%[^,],%[^,],%[^,],%d", qBuffer, ansBuffer1, ansBuffer2, ansBuffer3, ansBuffer4, iBuffer);

        //Storing data
        strcpy(question[count], qBuffer);
        strcpy(answer1[count], ansBuffer1);
        strcpy(answer2[count], ansBuffer2);
        strcpy(answer3[count], ansBuffer3);
        strcpy(answer4[count], ansBuffer4);
        correctAnswer[count] = iBuffer;

        // Check Correct Number of Items Read
        if( count == noOfQuestion )
        {
            printf("There are more items in the file than MaxNoItems specifies can be stored in the output arrays.\n\n");
            *size = count;
        }
        else if( count != *size - 1 )
        {
            printf("File is corrupted. Not as many items in the file as specified at the top.\n\n");
            *size = count;
        }
        //Break if reached end of file.
        if (feof(reader))
        { break;}
        }
        fclose(reader);
}
}

这是要读取的csv文件。每个问题和答案都在一行中。

What function do you use to open a file?,fscanf,fclose,fopen,main,3
Which of the following is not a variable type?,int,float,char,string,4
How many bytes is a character?,8,4,2,1,4
What programming language have you been studying this term?,B,A,D,C,4
Which of the following is a comment?,#comment,//comment,$comment,%comment,2
Which of these is in the C Standard Library?,stdio.h,studio.h,iostream,diskio.h,1
What tool do we use to compile?,compiler,builder,linker,wrench,1
What function do you use to close a file?,fscanf,fclose,fopen,main,2
How do you include a file?,#include,//include,$include,%include,1
What are you doing this quiz on?,paper,whiteboard,computer,chalkboard,3

Answer 1

我努力找到一种方法来解决代码中的问题，但是没有一种干净的方式来跟踪每行的双重读取，使其以合理的方式工作。您遇到的结构问题是尝试两次读取该行，首先确定大小，然后尝试读取实际值。这有很多陷阱。

不是试图以零碎方式读取每一行，而是使用由面向行的输入函数一次读取整行更好。 C（fgets，getline）。它将使您的代码更加灵活，并使您的生活更轻松。基本方法是一次读取一行到'缓冲区'，然后使用提供的工具，从行中提取您需要的内容，以有意义的方式存储它，然后继续下一行。

没有办法在函数参数列表中对一堆数组进行硬编码，并让它以一种理智的方式工作。正确的方法是将一个指向某个类型数据结构的指针传递给你的函数，让你的函数填充它，根据需要分配内存，并提供一个指针作为回报。在您的情况下，对于您希望阅读的每个问题，一个简单的结构更有意义，即一个二维数组。

define预期数字问题的初始大小（下面MAXQ 128）要好得多，并为该数量分配存储空间。您可以针对每个问题的预期答案执行相同的操作（下面为MAXA 16）。如果最终读取的数量超过每个，则可以轻松地重新分配以处理数据。

一旦您填写了struct（或array of structs），您就可以通过简单的返回将这些数据提供给您的主代码。然后，您可以使用指向数据的单个指针，您可以轻松地将打印功能传递给您，或者您需要数据的任何其他位置。由于数据的存储是动态分配的，因此您负责释放不再需要的内存。

我提供了打印和自由函数的示例，以说明将指针传递给函数之间的数据以及实际打印和释放内存。

从长远来看，以类似的方式设计代码将为您节省很多麻烦。有很多方法可以做到这一点，下面的例子只是一种方法。我评论了代码，以帮助您跟进。如果您有任何疑问，请查看并告诉我。

注意：我已将原始readQAs函数替换为我最初编写的版本，但问题仍然存在。使用getline时，您必须保留由getline 分配的任何缓冲区的起始地址，否则getline的重复调用将导致getline的段错误尝试重新分配其缓冲区。基本上，getline需要一种跟踪它所使用的内存的方法。只要您保留最初分配的缓冲区的起始地址，您就可以随心所欲地切换getline分配的缓冲区。保持指向原件的指针就足够了。

将缓冲区传递给对strtok或strsep等字符串进行操作的函数时，这可能会特别微妙。无论如何，未能保留由getline分配的缓冲区的开始的结果将导致segfault在任何循环耗尽由getline接收__memcpy_sse2 () from /lib64/libc.so.6分配的初始120字节缓冲区。如果你永远不会耗尽原始的120字节缓冲区，你将永远不会遇到段错误。底线，始终保留由getline分配的缓冲区的起始地址。

#include <stdio.h> #include <stdlib.h> #include <string.h> #define MAXQ 128 #define MAXA 16 typedef struct { char *q; char **ans; unsigned int nans; } ques; ques **readQAs (char *fn); void prn_ques (ques **exam); void free_ques (ques **exam); int main (int argc, char **argv) { if (argc < 2) { fprintf (stderr,"\n error: insufficient input. Usage: %s <csvfile>\n\n", argv[0]); return 1; } ques **exam = NULL; /* pointer to pointer to struct */ /* allocate/fill exam structs with questions/answers */ if ( !( exam = readQAs (argv[1]) ) ) { fprintf (stderr, "\n error: reading questions/answers from '%s'\n\n", argv[1]); return 1; } prn_ques (exam); /* print the questions/answers */ free_ques (exam); /* free all memory allocated */ return 0; } /* allocate and fill array of structs with questions/answers */ ques **readQAs (char *fn) { FILE *fp = fopen (fn, "r"); /* open file and validate */ if (!fp) { fprintf (stderr,"\n error: Unable to open file '%s'\n\n", fn); return NULL; } char *line = NULL; /* line buff, if NULL getline allocates */ size_t n = 0; /* max chars to read (0 - no limit) */ ssize_t nchr = 0; /* num chars actually read by getline */ char *p = NULL; /* general pointer to parse line */ char *sp = NULL; /* second pointer to parse line */ char *lp = NULL; /* line ptr (preserve line start addr) */ size_t qidx = 0; /* index for questions structs */ size_t aidx = 0; /* index for answers within structs */ ques **q = calloc (MAXQ, sizeof (*q)); /* allocate MAXQ ptrs */ if (!q) { fprintf (stderr,"\n Allocation error.\n\n"); return NULL; } /* for each line in file (fn) */ while ((nchr = getline (&line, &n, fp)) != -1) { /* test qidx = MAXQ-1, realloc */ aidx = 0; /* reset ans index each line */ lp = line; /* save line start address */ if (line[nchr - 1] == '\n') /* test/strip trailing newline */ line[--nchr] = 0; q [qidx] = calloc (1, sizeof (**q)); /* allocate struct */ q [qidx]-> ans = calloc (MAXA, sizeof (*(q[qidx]-> ans))); /* read question */ *(p = strchr (line, ',')) = 0; /* null-terminate ln at ',' */ q [qidx]-> q = strdup (line); /* alloc/read question */ sp = p + 1; /* sp now starts next ch */ /* read correct answer number */ *(p = strrchr (sp, ',')) = 0; /* null-term ln at last ',' */ q [qidx]-> nans = *(p+1) - '0'; /* save num ans, cvt to %zd */ /* read multi-choice answers */ for (p = strtok (sp, ","); p && *p; p = strtok (NULL, ",")) q [qidx]-> ans [aidx++] = strdup (p); /* alloc/read ans */ line = lp; /* avoid __memcpy_sse2 err */ qidx++; /* inc index for next Q */ } if (line) free (line); /* free line memory */ if (fp) fclose (fp); /* close file stream */ return q; /* return ptr to array of structs holding Q/A(s) */ } /* print formatted exam read from file */ void prn_ques (ques **exam) { if (!exam) { fprintf (stderr, "\n %s() error: invalid exam pointer.\n\n", __func__); return; } size_t qidx = 0; /* index for questions structs */ size_t aidx = 0; /* index for answers within structs */ printf ("\nClass Exam\n\n"); while (exam [qidx]) { printf (" %2zd. %s\n\n", qidx + 1, exam[qidx]-> q); aidx = 0; while (exam[qidx]->ans[aidx]) { if (exam[qidx]-> nans == aidx + 1) printf ("\t(%c) %-16s (* correct)\n", (int)aidx + 'a', exam[qidx]->ans[aidx]); else printf ("\t(%c) %s\n", (int)aidx + 'a', exam[qidx]->ans[aidx]); aidx++; } printf ("\n"); qidx++; } printf ("\n"); } /* free all memory allocated */ void free_ques (ques **exam) { if (!exam) { fprintf (stderr, "\n %s() error: invalid exam pointer.\n\n", __func__); return; } size_t qidx = 0; /* index for questions structs */ size_t aidx = 0; /* index for answers within structs */ while (exam[qidx]) { if (exam[qidx]->q) free (exam[qidx]->q); for (aidx = 0; aidx < MAXA; aidx++) { if (exam[qidx]->ans[aidx]) { free (exam[qidx]->ans[aidx]); } } free (exam[qidx]->ans); free (exam[qidx++]); } free (exam); }

<强>输出/验证

$ ./bin/readcsvfile dat/readcsvfile.csv Class Exam 1. What function do you use to open a file? (a) fscanf (b) fclose (c) fopen (* correct) (d) main 2. Which of the following is not a variable type? (a) int (b) float (c) char (d) string (* correct) 3. How many bytes is a character? (a) 8 (b) 4 (c) 2 (d) 1 (* correct) 4. What programming language have you been studying this term? (a) B (b) A (c) D (d) C (* correct) 5. Which of the following is a comment? (a) #comment (b) //comment (* correct) (c) $comment (d) %comment 6. Which of these is in the C Standard Library? (a) stdio.h (* correct) (b) studio.h (c) iostream (d) diskio.h 7. What tool do we use to compile? (a) compiler (* correct) (b) builder (c) linker (d) wrench 8. What function do you use to close a file? (a) fscanf (b) fclose (* correct) (c) fopen (d) main 9. How do you include a file? (a) #include (* correct) (b) //include (c) $include (d) %include 10. What are you doing this quiz on? (a) paper (b) whiteboard (c) computer (* correct) (d) chalkboard

valgrind验证：

==16221== ==16221== HEAP SUMMARY: ==16221== in use at exit: 0 bytes in 0 blocks ==16221== total heap usage: 73 allocs, 73 frees, 3,892 bytes allocated ==16221== ==16221== All heap blocks were freed -- no leaks are possible ==16221== ==16221== For counts of detected and suppressed errors, rerun with: -v ==16221== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)

c使用fscanf（）从文本文件中读取单独的单词

1 个答案: