C - 如何将文件的第二列存储在数组中？

Question

我有一个文件将数据存储在逗号分隔文件 (Countries.txt) 中，格式如下(这只是一个小样本):

AD,Andorra,AN,AD,AND,20.00,Andorra la Vella,Europe,Euro,EUR,67627.00
AE,United Arab Emirates,AE,AE,ARE,784.00,Abu Dhabi,Middle East,UAE Dirham,AED,2407460.00
AF,Afghanistan,AF,AF,AFG,4.00,Kabul,Asia,Afghani,AFA,26813057.00
AG,Antigua and Barbuda,AC,AG,ATG,28.00,Saint John's,Central America and the Caribbean,East Caribbean Dollar,XCD,66970.00
AI,Anguilla,AV,AI,AIA,660.00,The Valley,Central America and the Caribbean,East Caribbean Dollar,XCD,12132.00

我想存储每一行​​的第二个字段，这样我的数组只包含国家名称，如下所示:

char *countriesArray[4096];
countriesArray[0] = "Andorra"
countriesArray[1] = "United Arab Emirates"
countriesArray[2] = "Afghanistan"
countriesArray[3] = "Antigua and Barbuda"
countriesArray[4] = "Anguilla"

但每次我运行我的代码时，我的数组都没有正确填充。我很确定问题不在于标记算法，因为一旦我删除了 if 语句，我就可以正确显示每个标记。这是我的代码:

FILE * fp;
char * line = NULL;
size_t len = 0;

int count=0;
ssize_t read;
char *countriesArray[4096];

fp = fopen("Countries.txt", "r");
if (fp == NULL)
   exit(EXIT_FAILURE);

   while ((read = getline(&line, &len, fp)) != -1) 
   {
       printf("First while loop iterating");


       printf("%s", line);





       int index=0;
       char * pch;
       pch = strtok (line,",");
       int i;

       for (i=0; i<2; i++)
       {
           printf("Second while loop iterating");
           printf ("\npch is :%s\n",pch);


           if (index == 1)
           {    
               printf ("\nGoing to assign this to countriesArray:%s\n",pch);
               printf ("\nVariable count is:%d\n",count);
               countriesArray[count]=pch;
           }


           pch = strtok (NULL, ",");
           index++;




       }

       count++;


    }

    printf("countriesArray at index 0 is :%s\n", countriesArray[0]);
    printf("countriesArray at index 1 is :%s\n", countriesArray[1]);
    printf("countriesArray at index 2 is :%s\n", countriesArray[2]);
    printf("countriesArray at index 3 is :%s\n", countriesArray[3]);

    int i;
    for (i=0; i<count; i++)
    {
        free (countriesArray[i]);
    }

       if (line)
           free(line);
           exit(EXIT_SUCCESS);

输出:

First while loop iteratingAD,Andorra,AN,AD,AND,20.00,Andorra la Vella,Europe,Euro,EUR,67627.00
Second while loop iterating
pch is :AD
Second while loop iterating
pch is :Andorra

Going to assign this to countriesArray:Andorra

Variable count is:0
First while loop iteratingAE,United Arab Emirates,AE,AE,ARE,784.00,Abu Dhabi,Middle East,UAE Dirham,AED,2407460.00
Second while loop iterating
pch is :AE
Second while loop iterating
pch is :United Arab Emirates

Going to assign this to countriesArray:United Arab Emirates

Variable count is:1
First while loop iteratingAF,Afghanistan,AF,AF,AFG,4.00,Kabul,Asia,Afghani,AFA,26813057.00
Second while loop iterating
pch is :AF
Second while loop iterating
pch is :Afghanistan

Going to assign this to countriesArray:Afghanistan

Variable count is:2
First while loop iteratingAG,Antigua and Barbuda,AC,AG,ATG,28.00,Saint John's,Central America and the Caribbean,East Caribbean Dollar,XCD,66970.00
Second while loop iterating
pch is :AG
Second while loop iterating
pch is :Antigua and Barbuda

Going to assign this to countriesArray:Antigua and Barbuda

Variable count is:3
First while loop iteratingAI,Anguilla,AV,AI,AIA,660.00,The Valley,Central America and the Caribbean,East Caribbean Dollar,XCD,12132.00
Second while loop iterating
pch is :AI
Second while loop iterating
pch is :Anguilla

Going to assign this to countriesArray:Anguilla

Variable count is:4
countriesArray at index 0 is :Anguilla
countriesArray at index 1 is :Anguilla
countriesArray at index 2 is :Anguilla
countriesArray at index 3 is :Anguilla
*** Error in `./chef': free(): invalid pointer: 0x09c1c173 ***
Aborted (core dumped)

我是 C 编程的新手，所以请给我学习的机会!

EDIT :我取得了一些进展(见上面编辑过的代码)，现在我的变量 pch 和 count 在内部显示了正确的值if 语句。但是 countriesArray 仍然没有正确填充

Answer 1

您重复使用 getline 为 line 分配缓冲区，最后只释放一行。对于任何严重的程序，它都会导致所谓的内存泄漏:您分配了一 block 内存并丢失了允许释放它的指针。您应该有一个 char *lines[4096] 数组来保留所有这些行，以便能够在最后正确释放它们。

char *lines[4096];
while ((read = getline(&line, &len, fp)) != -1) 
{
    lines[count] = line;

在程序结束时:

for(int i=0; i<count; i++) {
    free(lines[i];
}

(仅此而已；不要尝试释放 countriesArray 元素，因为它们只是分配元素内的指针，分配的元素在行中)

但至少，您所有的 countriesArray 元素都指向不同的内存位置。

此代码中的真正问题是您在第一个循环之外将 index 设置为 0，例如 count。这对于 count 是正确的，但在第一个循环的每次迭代中必须将索引重置为 0。