Segmentation fault while running the binary file copied by C program

Question

I have a C program to copy the Binary file of a compiled (executable) "Hello World!" program.

Below is its code.

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

int main()
{
    /* File pointer for source and target files. */
    FILE *fs, *ft;
    char ch;

    /* Open the source file in binary read mode. */
    fs = fopen("a.out","rb");
    if (fs == NULL)
    {
        printf("Error opening source file.\n");
        exit(1);
    }

    /* Open the target file in binary write mode. */
    ft = fopen("hello","wb");
    if (ft == NULL)
    {
        printf("Error opening target file.\n ");
        fclose(fs);
        exit(2);
    }

    while((ch = fgetc(fs)) != EOF)
    {
        fputc(ch, ft);
    }

    fclose(fs);
    fclose(ft);
    return 0;
}

I have compiled to above program and gave the executable name 'file10'.

a.out is the executable (binary) of a hello world program.

-bash-4.1$ ./a.out
Hello World!
-bash-4.1$

Now I run the above program so that a.out will be copied to "hello" binary file.

-bash-4.1$ ./file10
-bash-4.1$

This creates the binary file "hello".

Next I try to run this binary file.

-bash-4.1$ ./hello
-bash: ./hello: Permission denied
-bash-4.1$

I get permission denied. Next I change the permissions.

-bash-4.1$ chmod 777 hello
-bash-4.1$

Now when I run "hello" I get a segmentation fault.

-bash-4.1$ ./hello
Segmentation fault
-bash-4.1$

Why is there a segmentation fault? Can't executable of C program be copied like how I did in the program above?

Thanks.

R.. GitHub STOP HELPING ICE · Accepted Answer · 2015-02-15 04:38:10Z

4

Your variable ch has the wrong type. It should have type int, not char. By storing the result of fgetc into a char, you're collapsing the values 255 and EOF into a single value and thus stopping the first time you encounter a byte with value 255.

answered Feb 15, 2015 at 4:38

R.. GitHub STOP HELPING ICE

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2 Comments

bare_metal Over a year ago

but still it is not clear as how this causes a segfault?

M.M Over a year ago

@bare_metal what do you expect to happen when you cut off an executable partway through and then run it ??

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