Why is this function not copying the input file? - c

Question

I'm just getting started into file I/O and am trying to build a function that will simply copy a file to destination.
This program compiles however an empty file is created and nothing is copied. Any advice?
#include <stdio.h>
int copy_file(char FileSource[], char FileDestination[]) {
char content;
FILE *inputf = fopen(FileSource, "r");
FILE *outputf = fopen(FileDestination, "w");
if (inputf == NULL)
;
printf("Error: File could not be read \n");
return;
while ((content = getc(inputf)) != EOF) putc(content, inputf);
fclose(outputf);
fclose(inputf);
printf("Your file was successfully copied");
return 0;
}
int main() {
char inputname[100];
char outputname[100];
printf("Please enter input file name: \n");
scanf("%s", &inputname);
printf("Please write output file name: \n");
scanf("%s", &outputname);
copy_file(inputname, outputname);
return 0;
}

Answer 1

There are few bugs in the code you mentioned. These two below statement
scanf("%s", &inputname);
scanf("%s", &outputname);
Are wrong as inputname and outputname are char array and array name itself address so you no need to give &inputname to scanf(). For e.g
scanf("%s",inputname);
scanf("%s",outputname);
Also ; at the end of if statement is not serving correct purpose as you expected.
This
if(inputf == NULL);
Should be
if(inputf == NULL){
/*error handling */
}
As pointed by other, getc() returns int not char. From the manual page of getc()
int getc(FILE *stream);
And this
putc(content, inputf);
Change to
putc(content, outputf); /* write the data into outputf */

Answer 2

Your line :
putc(content, inputf);
needs to change to
putc(content, outputf);

Answer 3

This code has a lot of problems:
if(inputf == NULL);
printf("Error: File could not be read \n");
return;
It is the equivalent of
if(inputf == NULL)
{
;
}
printf("Error: File could not be read \n");
return;
You have a stray ; that terminates you if statement, and whitespace doesn't matter much at all with C.
So your if statement does nothing, and your code will always emit the "Error: File could not be read" message and return without doing anything else.
What you probably want:
if(inputf == NULL)
{
printf("Error: File could not be read \n");
return;
}
This is a perfect example of why a lot of C programmers always use braces after if statements. ALWAYS.

Answer 4

There are multiple problems in your code:
content must be declared as int: getc() returns an int with the value of the byte read from the file or the special negative value EOF at end of file. Storing that to a char variable loses information, making the test for EOF either ambiguous (if char is signed) or always false (if char is unsigned by default).
you should pass outputf to putc.
you should return from the copy_file function if fopen fails to open either file.
you should pass the maximum number of characters to read for the filenames
you should check the return value of scanf() to avoid undefined behavior on invalid input.
Here is a corrected version:
#include <stdio.h>
int copy_file(const char *FileSource, const char *FileDestination) {
int content;
FILE *inputf, *outputf;
if ((inputf = fopen(FileSource, "r")) == NULL) {
printf("Error: cannot open input file %s\n", FileSource);
return -1;
}
if ((outputf = fopen(FileDestination, "w")) == NULL) {
printf("Error: cannot open output file %s\n", FileDestination);
fclose(inputf);
return -1;
}
while ((content = getc(inputf)) != EOF)
putc(content, inputf);
fclose(outputf);
fclose(inputf);
printf("Your file was successfully copied");
return 0;
}
int main() {
char inputname[100];
char outputname[100];
printf("Please enter input file name: \n");
if (scanf("%99s", inputname) != 1)
return 1;
printf("Please write output file name: \n");
if (scanf("%99s", &outputname) != 1)
return 1;
copy_file(inputname, outputname);
return 0;
}

Answer 5

Use sendfile() is more simple and efficient for copying file. You can view more detail about sendfile() by man sendfile.
#include <stdio.h>
#include <string.h>
#include <sys/sendfile.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
if (argc < 3)
{
printf("Usage: %s <srcfile> <dst_file>\n", argv[0]);
return 1;
}
char *src_file = argv[1];
char *dst_file = argv[2];
int src;
int dst;
ssize_t size;
struct stat stat_buf;
if ((src = open(src_file, O_RDONLY)) < 0)
{
printf("Can not open %s\n", src_file);
return -1;
}
if (fstat(src, &stat_buf) < 0)
{
printf("Can stat %s\n", src_file);
close(src);
return -2;
}
if ((dst = open(dst_file, O_CREAT|O_WRONLY, stat_buf.st_mode)) < 0)
{
printf("Can not open %s\n", dst_file);
return -1;
}
if ((size = sendfile(dst, src, NULL, stat_buf.st_size)) < 0)
{
printf("Fail to copy file, size: %ld\n", size);
}
else
{
printf("Success, size: %ld\n", size);
}
close(src);
close(dst);
return 0;
}