读取文本文件值

Question

I've got the below code and am trying to read a text file which is comma delimited and need to grab the values. The text file (out.txt) contains 2 numbers:

12.4,45.8

My code is:

#include <stdlib.h>
#include<stdio.h>

int main()
{
    system("python Grab_Values.py > out.txt");

    FILE *ptr_file;
    char buf[1000];
    int v1;
    int v2;

    ptr_file =fopen("out.txt","r");
    if (!ptr_file)
            return 1;
    while (fgets(buf,1000, ptr_file)!=NULL)
            fscanf(buf, "%d,%d\n", &v1, &v2);

    fclose(ptr_file);
    printf("%d" "\n", v1);
    return 0;
}

When compiling I get the following errors:

test.c: In function âmainâ:
test.c:17:10: warning: passing argument 1 of âfscanfâ from incompatible pointer type [enabled by default]
/usr/include/stdio.h:445:12: note: expected âstruct FILE * __restrict__â but argument is of type âchar *â

I am still ac noob so its probably a simple error but I can't figure out what :(

Answer 1

You're using 'fscanf', which is used to read from a file. I think you want to use 'sscanf' to read the input from the 'buf' char array you read the file content into.

Bonus points - you could actually just use fscanf and do away with the 'fgets'.

Answer 2

The error in the code is here,

fscanf(buf, "%d,%d\n", &v1, &v2); 

fscanf() expects a FILE* , or more clearly a stream but you are giving a character pointer..

You can use sscanf() instead, if you wanna read from character pointer

Answer 3

Three things are wrong with this one:

while (fgets(buf,1000, ptr_file)!=NULL)
        fscanf(buf, "%d,%d\n", &v1, &v2);

1. fgets already reads data, so it's not longer available for fscanf
2. you use %d as format specifier (integer), but you want to read float values (also change the type of v1 and v2 !)
3. The first argument of fscanf is the file stream, so you need to provide ptr_file there.

So change it to:

fscanf(ptr_file, "%f,%f", &v1, &v2);

But also note, that this text format might not work with other locales, where the comma is the decimal point! You should consider enclosing comma separated float values by quotation marks.