为什么我不能从文件中读取？

Question

I'm trying to read few bytes from a file and then print them to screen, but the read() function keeps returning -1 for some reason.

Here's the code:

#include<stdio.h> 
#include<sys/types.h> 
#include<fcntl.h>
#include<stdlib.h> 

int main(int argc, char* argv[]) {

    char buff[100];

    int file_desc=open(argv[1], O_RDONLY);
    if (file_desc<0) {
        printf("Error opening the file.\n");
        exit(-1);
    }
    printf("File was successfully opened with file descriptor %d.\n", file_desc);


    int ret_code=read(argv[1],buff,20);
    if (ret_code==-1) {
        printf("Error reading the file.\n");
        exit(-1);
    }

    int i;
    for (i=0; i<20; i++) {
        printf("%c ",buff[i]);
    }
    printf("\n");
}

The output for this is:

File was successfully opened with file descriptor 3.
Error reading the file.

The file I'm trying to read from is definitely bigger than 20 bytes.
What could be the problem here?

Answer 1

If you look at the parameters for read , the first parameter should be the open file descriptor, not the file name;

int ret_code=read(file_desc,buff,20);

...should work better.