c: reading from files

Question

In this function findBookByTitle what is supposed to happen is fp is opened and if a title matches the one given to function it will print the title. It is assumed titles are unique so once a match is found it can stop searching. My problem is i'm not entirely sure how to match the title to something in a file. This is what I have so far...

    void findBookByTitle(FILE* fp, char title[])
    {
       FILE * fp = fopen(fp, "r");
       while(!EOF && *fp = title){
          printf("Title: <%c> \n", title);
       }
       if(EOF && *fp != title ){
          printf("No books match the title: <%c> ", title);
       }
    }

As well when I compile I get a few errors, it might be pointless to address these as my function remains incomplete but a few of these really confuse me.

34: error: 'fp' redeclared as different kind of symbol 32: note: previous definition of 'fp' was here 34: warning: passing argument 1 of 'fopen' from incompatible pointer type /usr/include/stdio.h:251: note: expected 'const char * restrict ' but argument is of type 'struct FILE *' 35: error: invalid operands to binary && (have 'int' and 'FILE') 38: error: invalid operands to binary != (have 'FILE' and 'char *')

Answer 1

1. Your function is declared as taking a FILE * as its first argument, but it then proceeds to treat that argument as if it's a filename and try to open another FILE * (with the same name!) using it. Make up your mind on whether the argument is a FILE * or a char * , and change your code accordingly.

2. You are trying to use EOF to test for EOF on fp . It's not quite that simple. Try feof(fp) instead.

3. You are trying to read from fp using *fp = title (and *fp != title ). This doesn't make any sense at all. You need to use a function to read from the file pointer, such as fgets or fscanf .

Answer 2

You are overwriting the value in your file pointer with a pointer to a char when you use assignment like that ( *fp = title ). After that all kinds of problems will happen.

You probably also need to remove the line:

   FILE * fp = fopen(fp, "r");

Since you already have a FILE * fp isn't the name of a file to open. It's an already opened file.

Answer 3

1. You have FILE *pt twice
2. You can't compare a FILE pointer with a string ( char * )
3. You can't output a string with the option %c
4. EOF is -1 and with the operator ! this is true if EOF is 0 but EOF will never change
5. Your algorithm is strange

The right code should be right (so far I've understand your problem):

#include <stdio.h>
#include <string.h>

void findBookTitle(char *path, char **title, int titles) {
    FILE *fp = fopen(path, "r");
    char line[100];
    int i = 0, count = 0;
    while (fgets(line, 100, fp) != NULL) {
        while (i < titles)
            if (!strcmp(title[i], line)) {
                printf("Title: <%s>\n", line);
                count++;
            }
        i = 0;
    }
    if (!count)
        printf("No books found.\n");
}