Reading 2 byte at a time from a binary file - c

Question

I have an elf file that called example. I wrote following code which it's read the content of the example file in the binary mode and then I wanted to save their content in another file called example.binary. But when I run the following program it shows me a segmentation fault. What's wrong with this program? I can't find out my mistake.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
// typedef macro
typedef char* __string;
//Function prototypes
void readFileToMachine(__string arg_path);
int main(int argc, char *argv[]) {
__string pathBinaryFile;
if(argc != 2){
printf("Usage : ./program file.\n");
exit(1);
}
pathBinaryFile = argv[1];
readFileToMachine(pathBinaryFile);
return EXIT_SUCCESS;
}
void readFileToMachine(__string arg_path){
int ch;
__string pathInputFile = arg_path;
__string pathOutputFile = strcat(pathInputFile, ".binary");
FILE *inputFile = fopen(pathInputFile, "rb");
FILE *outputFile = fopen(pathOutputFile, "wb");
ch = getc(inputFile);
while (ch != EOF){
fprintf(outputFile, "%x" , ch);
ch = getc(inputFile);
}
fclose(inputFile);
fclose(outputFile);
}

Answer 1

You have no room to concatenate extention to path so you have to create space for that.
One solution could be:
char ext[] = ".binary";
pathOutputFile = strdup(arg_path);
if (pathOutputFile != NULL)
{
pathOutputFile = realloc(pathOutputFile, strlen(arg_path) + sizeof(ext));
if (pathOutputFile != NULL)
{
pathOutputFile = strcat(pathInputFile, ext);
// YOUR STUFF
}
free(pathOutputFile);
}
Side note: typedef a pointer is not a good idea...

Answer 2

change your typedef to typedef char* __charptr
void rw_binaryfile(__charptr arg_path){
FILE *inputFile;
FILE *outputFile;
__charptr extension = ".binary";
__charptr pathOutputFile = strdup(arg_path);
if (pathOutputFile != NULL){
pathOutputFile = realloc(pathOutputFile, strlen(arg_path) + sizeof(extension));
if (pathOutputFile != NULL){
pathOutputFile = strcat(pathOutputFile, ".binary");
inputFile = fopen(arg_path, "rb");
outputFile = fopen(pathOutputFile, "wb");
write_file(inputFile, outputFile);
}
}
}
void write_file(FILE *read, FILE *write){
int ch;
ch = getc(read);
while (ch != EOF){
fprintf(write, "%x" , ch);
ch = getc(read);
}
}