CODEWITHSUNDEEP
cfileloopspointerswhile-loop
WOW
WOW

Reputation: 99

How to traverse C loop correctly using File Pointer only

I am making a program in c that reads line by line and does some operation on the elements of every line. I am calling my read_row function like this.

while(filePointer!=NULL)
{
        int result=readRow(filePointer,headerRow,lineRow);
        printf("The value of  row is |%d|\n",result);
}

Inside my read_row function I am using get c to traverse through the line.

 cc=getc(fp);
    while((cc!='\n') && (cc!= EOF))
    {

            *line=cc;
            line++;  
            if(cc==',')
            {
                counterr++;
            }
            cc=getc(fp);

    }  

    if(cc==EOF)
    {
        fp=NULL;
    }

I am trying traverse through all the lines. However, this loop is infinite as file pointer never goes to null. I have tried to set the file pointer to null if the cc equals to EOF. However, this did not help at all. Therefore, please explain how should I properly terminate that loop. I believe that '\n' is coming before the EOF.Therefore, the file pointer is not getting to null. I have to do it using the file Pointer, as I have already made a very big program based on that logic. Moreover, I could only find examples that used methods like fgets() to traverse.

Upvotes: 1

Views: 1383

Answers (3)

jinbo.ma
jinbo.ma

Reputation: 1

You may use this function to try：

fscanf(fp,"%s\n",out_buffer)

Upvotes: 0

user3629249
user3629249

Reputation: 16540

the posted code has several significant errors.

For instance setting the parameter `FILE* fp = NULL; is only changing the copy of the actual fp, not the fp back in the calling function.

after the FILE * fp parameter is changed to FILE **fp and the call to the function is modified to match:

before modifying the fp, pass that parameter to fclose(*fp) otherwise the file is still open but the pointer to the associated file descriptor is destroyed, so the file cannot be closed.

Upvotes: 0

SingerOfTheFall
SingerOfTheFall

Reputation: 29976

When you pass a pointer to the function and then change it, you are actually changing the copy of that pointer, not the pointer itself. You need to pass a pointer to pointer for this to work, here's a small example:

int a = 2;
int b = 5;

//note the pointer to pointer:
void foo(int **ptr)
{
    *ptr = &b;
}

int main() {
    int * ptr = &a;
    foo(&ptr);
    printf("%d", *ptr); // prints 5
}

So in your case the readRow should accept FILE**, and you should call it as readRow(&filePointer...

Upvotes: 7

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