How to read a regular text file? - c++

Question

I am trying to write a program will open a regular type file (binary or text/ASCII, read every byte in the file and write both the ASCII hex value for that byte as well as it’s printable (human-readable) character (characters, digits, symbols) to standard output. I am now just trying to let the user pick the file.
#include <stdio.h>
#include<stdlib.h>
FILE *file;
int main(int argc, char *argv[ ]){
int a;
int modified = 1;//1 means unmodified, 0 means modified
if(argc > 2){//writes to std error output
return 25;
}
if(argc == 2){// if there is 1 argument open it and read it
file = fopen(argv[1], "rt");
if(file == NULL){//cant open file. return error code 15
fprintf(stderr, "cant opent file %s \nerror code 15 \n", argv[1]);
return 15;
}
a = getc(file);
}else// get characters from stdin if no arguments
a = getchar();
char *buffer = malloc(200);
int j = 0;// buffer index helper
while( a != EOF){//reads character by character until EOF
if(j > 200){
j =0;
// fprintf(stderr,"error error, buffer overflow. \n error code 35 \n"); // send error to stderrl
// return 35;
}
I am getting errors though:
error: invalid conversion from `void*' to `char*'
xsd.cpp:30: error: expected `}' at end of input
xsd.cpp:30: error: expected `}' at end of input

Answer 1

The major problem is that you write C in a C++ program. C and C++ are similar, due to C++ inheriting from C, but they are ultimately different languages. For example, C++ have a harder and tougher type system, so you can't e.g. have implicit cast from void * to other pointer types like you can in C. In C++ you have to cast void * to the correct pointer, like e.g.
char *buffer = reinterpret_cast<char*>(malloc(200));
Even better would be to not write C code in C++, and use the C++ functionality like new/delete, the C++ input/output library, and classes like std::string for strings, etc.
Then there's of course the problem of you not having enough closing braces } at the end of the program. Did you not copy-paste all of the program?