Passing in filename from command line to read file content

Question

I have a function ./transform that needs to take in two command line arguments for an input and output file.

Like so: ./transform "inputfile" "outputfile"

I am then trying to read the file using fopen to store each character in the file into a character array char token[1024]. The total number of characters in the input file will always be <= 1024.

I am receiving errors about fopen not having the right amount of arguments. Here is pseudo-code of what I am trying to accomplish.

void main(FILE *inputFile, FILE *outputFile){
    char token[1024];
    token = fopen(&inputFile, "r");
}

Yes, I am aware I am trying to assign a FILE value to a Char value... I wrote it this way to show that I want each character from the inputFile stored in the character array. I am unsure how to do so properly. After executing the program's code (converting hex and int values from file to ASCII), I need to save the converted ASCII text into the user-defined output file.

Answer 1

There are few issues with the code you tried, firstly here

void main(FILE *inputFile, FILE *outputFile){ }

you are trying to change prototype of main() which is not correct. According to C Standard Section 5.1.2.2.1 Program startup, either it should be

int main(void) { /* ... */ }

or

int main(int argc, char *argv[]) { /* ... */ }

So make it like

int main(int argc, char *argv[]) {
    /*some_code */
}

Next, to open a file using fopen() from command line, this

token = fopen(&inputFile, "r");

is completely wrong as fopen() returns argument of FILE* not char* & argument you provided to fopen() also wrong. Read then manual page of fopen() ,it says

FILE *fopen(const char *path, const char *mode);

Sample code

int main(int argc, char *argv[]) {
  if( argc!= 3 ) { /*if user input is not correct, inform user */
     printf("./transform inputfile outputfile \n");
     return 0;
  }
  FILE *fp = fopen(argv[1],"r); 
  if(fp == NULL) {
     /* error handling */
     return 0;
  }
  /* do_stuff_with_fp */  
}