remove /* */ and // comments in C programming language

rm_comments.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

/*
 * @after_rm_comments_buf - buffer for removed file
 * @src_file_name - source file for removing comments
 * @return number of removed comments
 */
int rm_all_comments(char *after_rm_comments_buf, char *src_file_name);

/*
   To execute the program, pass arguments like this:
   ./a.out src_file_for_removing_comments result_file_name

   remark: result_file_name is exists does not matter
*/
int main(int argc, char *argv[]){
    char *src_file_name = argv[argc - 2];
    char *dest_file_name = argv[argc - 1];
    int fd;

    fd = open(src_file_name, O_RDONLY);
    if(fd == -1){
        printf("%s\n", strerror(errno));
        return EXIT_FAILURE;
    }

    ssize_t buf_size;
    buf_size = lseek(fd, 0, SEEK_END);
    if(buf_size == -1){
        printf("%s\n", strerror(errno));
        return EXIT_FAILURE;
    }

    close(fd);

    fd = open(dest_file_name, O_CREAT | O_WRONLY, 0777);
    if(fd == -1){
        printf("%s\n", strerror(errno));
        return EXIT_FAILURE;
    }

    char result[buf_size];
    int comments_cnt = rm_all_comments(result, src_file_name);
    
    ssize_t write_size;
    write_size = write(fd, result, strlen(result));
    if(write_size == -1){
        printf("%s\n", strerror(errno));
        return EXIT_FAILURE;
    }
    printf("removed total %d comments\n", comments_cnt);
    
    close(fd);
    return EXIT_SUCCESS;
}

int rm_all_comments(char *after_rm_comments_buf, char *src_file_name){
    FILE *file_ptr = fopen(src_file_name, "r");
    if(file_ptr == NULL)
        return -1;
    
    int c;
    int c1;
    size_t idx = 0;
    size_t comments_cnt = 0;

    while((c = getc(file_ptr)) != EOF){
        if(c == '/'){
            check_again:
                if((c1 = getc(file_ptr)) == EOF)
                    goto end;
                else if(c1 != '*' && c1 != '/')
                    goto insert;
                
                // invariant: a comment is found
                comments_cnt++;

                if(c1 == '/'){
                    // a double back slash comment is found
                    while((c = getc(file_ptr))){
                        if(c == EOF)
                            goto end;
                        else if(c == '\n')
                            goto insert;
                    }
                }
                
                // a /* */ comment is found
                while((c1 = getc(file_ptr)) != '*' || (c1 = getc(file_ptr)) != '/');
                
                // skip '/'
                c = getc(file_ptr);
                if(c == '/')
                    goto check_again;
        }

        insert:
            after_rm_comments_buf[idx++] = c;
    }
    after_rm_comments_buf[idx] = '\0';

    end:
        fclose(file_ptr);
        return comments_cnt;
}