打印目录C程序中所有文件的内容

Question

Hello and good evening,

I'm making a program that will gather all the files in a given directory and print out all of the integers inside them.

This is homework but not THE homework. This is a small part of it that I can't figure out.

Here's the code:

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <dirent.h>
#include <unistd.h>
#include <stdlib.h>
#include "mergefiles.c"

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

if(2 != argc)
{
    printf("Directory name missing!\n");
    return 0;
}
DIR *dp = NULL;
struct dirent *dptr = NULL;
FILE *input_file;
FILE *next_file;
char c;

if (NULL == (dp = opendir(argv[1])))
{
    printf("Cannot open the given directory %s", argv[1]);
    exit(1);
}
else
{
    while(NULL != (dptr = readdir(dp)))
    {
        if(!strcmp (dptr->d_name, "."))
        {
            continue;
        }
        if(!strcmp (dptr->d_name, ".."))
        {
            continue;
        }

        input_file = fopen(dptr->d_name, "r");
        if(input_file == NULL)
        {
            perror("Cannot open file or no file exists\n");
            fclose(input_file);

            return 0;
        }
        c = fgetc(input_file);
        while(c != EOF)
        {
            printf("%d", c);
        }
        printf(%s\n", dptr->d_name);
    }
    closedir(dp);
}
return 0;
}

I started with this slowly. First, I read a directory. Then I printed the names of all the files within the directory. All of that works just fine (which is really cool!).

However, i'm getting a segfault whenever I try to do the fclose(input_file) within the first while loop . At first, I thought it was because there was nothing in the file (I fixed this by putting something in the file), but that doesn't work.

Strangely, when I take out the fclose(input_file) , it will compile, but throw out the second error: Cannot open file or file doesn't exist .

All the files contain integers, one on each line, of varying depth. I did my best to proofread the code so if there are any errors (typo's and such) let me know and I'll edit it right away.

Thanks for any all words of wisdom. :D

Update:

So I get a segfault because the input_file is NULL and I'm trying to close it...which makes sense and I can't believe I missed it.

What I don't understand is why the input_file is NULL in the first place.

Answer 1

The reason why you get input_file equal to NULL is obvious, because there is no such file that you want to open is in the current directory.

Suppose for example consider your working directory as (this is where you are compiling your C program)

/home/student/Myfolder

Let us assume you want to open "Input" folder and there are two files 1.txt and 2.txt.

After compiling what compiler does for fopen() is it searches for file as

/home/student/Myfolder/1.txt

But the actual path is

/home/student/Myfolder/Input/1.txt

I hope you understand that. To overcome this you have to get the current working directory cwd() function and then append the directory name and file name. Below is the complete program. Please do note the commands I have made in the program.

#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <dirent.h>
#include <unistd.h>
#include <stdlib.h>

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

if(2 != argc)
{
    printf("Directory name missing!\n");
    return 0;
}
DIR *dp = NULL;
struct dirent *dptr = NULL;
FILE *input_file;
FILE *next_file;
char c,cwd[256]; //created new character array

if (NULL == (dp = opendir(argv[1])))
{
    printf("Cannot open the given directory %s", argv[1]);
    exit(1);
}
else
{
    while((dptr = readdir(dp))!=NULL)
    {
        if(!strcmp (dptr->d_name, "."))
        {
            continue;
        }
        if(!strcmp (dptr->d_name, ".."))
        {
            continue;
        }
    if(getcwd(cwd, sizeof(cwd)) == NULL) //this is important
    {
        printf("No such file or directory");
        continue;
    }
    if(dptr->d_name[0]=='.')  //Files never begin with '.' 
        continue;
    strcat(cwd,"/");   //For windows "\"
    strcat(cwd,argv[1]);
    strcat(cwd,"/");   //For windows "\"
    strcat(cwd,dptr->d_name);
    printf("%s",cwd);  //check for working directory
        input_file = fopen(cwd, "r");
    printf("%s\n",dptr->d_name); //validation check
        if(input_file == NULL)
        {
            perror("Cannot open file or no file exists\n");
            fclose(input_file);
            return 0;
        }
        c = fgetc(input_file);
        while(c != EOF)
        {
            printf("%d", c);
        }
        printf("%s\n", dptr->d_name);
    }
    closedir(dp);
}
return 0;
}