I'm having issues with an assignment where I have to take the contents of one file into a buffer, reverse those contents, and write them to another file. This program NEEDS to utilize two functions that look like this:
int read_file( char* filename, char **buffer );int write_file( char* filename, char *buffer, int size);so far my files look like this:
file_utils.h
#ifndef UTILS_H
#define UTILS_H
int read_file(char* filename, char **buffer);
int write_file(char* filename, char *buffer, int size);
#endif
file_utils.c
#include "file_utils.h"
#include <stdlib.h>
#include <stdio.h>
#include <font1.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
int read_file(char* filename, char **buffer) {
FILE* file1;
file1 = fopen(filename, "r");
//gets the size of the file
struct stat st;
stat(filename, &st);
int size = st.st_size;
buffer = malloc(size);
read(file1, &buffer, 1);
return size;
}
int write_file(char* filename, char*buffer, int size) {
FILE* file2;
file2 = fopen(filename, 'w');
for (int k = size - 1; k >= 0; k--) {
char* x = &buffer + k;
fprintf(file2, "%s", x);
}
printf(filename, '\O');
return 1;
}
reverse.c
#include "file_utils.h"
#include <stdlib.h>
#include <stdio.h>
#include <font1.h>
#include <string.h>
#include <sys/stat.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
char* buffer;
char* filename1;
char* filename2;
int filesize;
filename1 = argv[1];
filename2 = argv[2];
filesize = read_file(filename1, &buffer);
write_file(filename2, buffer, filesize);
return 0;
}
and that's all there is. I run it using "clang file_utils.c reverse.c" and I get warnings for file_utils.c like
incompatible integer to pointer conversion passing 'int" to parameter of type 'const char *' (for the line file1 = fopen(filename, 'r')incompatible pointer to integer conversion passing 'FILE *' (aka 'struct_IO_FILE*') to parameter of type 'int' (for the line read(file1, &buffer, 1);)incompatible pointer types initializing 'char *' with an expression of type 'char **'; dereferences with * (for the line char* x = &buffer + k;)on top of all this when I continue on to run the executable as such
./a.out file1 file2
where file 1 has text that should be reversed into file 2, I get a segmentation fault.
Any insight into things I can fix will be much appreciated.
Just off the top of my head, without testing, I see these bugs:
buffer = malloc(size); should be *buffer = malloc(size);
... because buffer is a pointer to pointer to char, you need to
dereference it once.
read(file1, &buffer, 1); should be fread(*buffer, 1, size, file1);
... because you opened file1 with fopen, so it's FILE *. read is
Unix I/O, not stream I/O, and doesn't use FILE *.
file2 = fopen(filename, 'w'); should be file2 = fopen(filename, "w");
The second argument should be a "string" (pointer to char or array of
char). 'w' is a single char.
char* x = &buffer + k; should be char *x = buffer + k;
buffer is a pointer to char, so you want to use it directly, not
take its address. Also note the style of putting * next to the
variable instead of the type. This is a good habit, because these
do not mean the same thing:
char *a, *b, *c; /* three pointers */
char* a, b, c; /* one pointer, two chars */
fprintf(file2, "%s", x); should be fprintf(file2, "%c", *x);
The first form treats x as the beginning of a string and will output
everything from that point onward until it hits a NUL terminator. You
want to output only one char, so use the %c specifier, and
dereference x to get a char.
A better way would be fwrite(x, 1, 1, file2);
printf(filename, '\O'); is not needed and doesn't do what you think.
It looks like you intended to write a NUL at the end. That would be
'\0' (zero), not '\O' (letter O). In any case, it's not needed or
wanted. NUL is used to terminate a string in C, not a file. Your output
file will be one character longer than it should be if you do this.