Thread: old c compiler project

In this old c code it would not compile. I did change the old style main() parameter listing to the newer form. Then I noticed that there several functions being called before they were defined so I cut and pasted in function prototypes before main()! Still work to do. The compiler complained about missing libraries so I added in the appropriate headers and now the project compiles and actually runs.
In the code line
BOOLEAN get_source_line();
the compiler gives the following warning messages:

[Warning] empty parentheses were disambiguated as a function declaration [-Wvexing-parse]

[Note] remove parentheses to default-initialize a variable
[Note] or replace parentheses with braces to value-initialize a variable
Anyone know what this is about?

Filenames in capitals (especially the .C bit) are assumed to be C++ programs.

Code:

$ gcc LIST.C 
LIST.C:63:1: warning: ISO C++ forbids declaration of ‘main’ with no type [-Wreturn-type]
   63 | main(int argc, char** argv)
      | ^~~~
LIST.C: In function ‘int main(int, char**)’:
LIST.C:65:28: warning: empty parentheses were disambiguated as a function declaration [-Wvexing-parse]
   65 |     BOOLEAN get_source_line();
      |                            ^~
LIST.C:65:28: note: remove parentheses to default-initialize a variable
   65 |     BOOLEAN get_source_line();
      |                            ^~
      |                            --
LIST.C:65:28: note: or replace parentheses with braces to value-initialize a variable

If you force the compiler to treat it as a C program, this happens.

Code:

$ gcc -x c LIST.C 
LIST.C:23:10: fatal error: cstring: No such file or directory
   23 | #include <cstring>
      |          ^~~~~~~~~
compilation terminated.

Fixing your C++ headers to be C headers, you're almost there.

Code:

$ gcc -x c LIST.C 
LIST.C:63:1: warning: return type defaults to ‘int’ [-Wimplicit-int]
   63 | main(int argc, char** argv)
      | ^~~~

Originally Posted by maxcy

In this old c code it would not compile. I did change the old style main() parameter listing to the newer form. Then I noticed that there several functions being called before they were defined so I cut and pasted in function prototypes before main()! Still work to do. The compiler complained about missing libraries so I added in the appropriate headers and now the project compiles and actually runs.
In the code line
BOOLEAN get_source_line();
the compiler gives the following warning messages:

[Warning] empty parentheses were disambiguated as a function declaration [-Wvexing-parse]

[Note] remove parentheses to default-initialize a variable
[Note] or replace parentheses with braces to value-initialize a variable
Anyone know what this is about?

Those strcpy calls are buffer-overflows just waiting to happen. Save yourself the headache and use strncpy.

The program should not segfault when called without arguments either. Print a "usage" message and exit with a non-zero value.

The "levels" variable is also never used, so it will always be zero. (I presume the original author was planning on counting indention levels but never actually finished implementing the feature?) So that could be removed from the program entirely.

Adding to what Salem and Galahad have said:

You are mixing tabs and spaces for indentation. Just use one or the other. Spaces are best.

Not only should you check that argc is 2 to ensure a parameter has been provided, you should also check that the FILE* is not NULL after trying to open the file.

No need to strcpy argv[1] to another buffer. If you want a better name for it, just do:
const char *source_name = argv[1];

No need to copy the 'source_buffer' to the 'print_buffer' just to add the line number. Just print the line number before the line in the printf statement.

The whole 'save_ch', 'save_chp' thing is not well thought out. If the line is too long the printf("%s", line) call will not print a newline (left in the buffer by the fgets). Also, the rest of the line is just thrown away.

The 'while (get_source_line()) ;' structure is kind of dumb and part of the reason there are so many globals. It would probably be better to put the whole program in main.

The "BOOLEAN get_source_line();" problem is caused by having that declaration in main for no purpose (and compiling it as C++). Just remove it.

Here's a rewrite. Still not perfect, though.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
 
#define MAX_SOURCE_LINE 1024
#define MAX_PRINT_LINE    74  // leave room for line number
#define MAX_DATE_STRING   32
#define LINES_PER_PAGE    50
 
int main(int argc, char **argv) {
    if (argc != 2) {
        fprintf(stderr, "Usage: lister SOURCE_FILE");
        exit(EXIT_FAILURE);
    }
 
    const char *source_name = argv[1];
 
    FILE *file = fopen(source_name, "r");
    if (!file) {
        perror("Error: cannot open file");
        exit(EXIT_FAILURE);
    }
 
    char date[MAX_DATE_STRING];
    time_t timer;
    time(&timer);
    strcpy(date, asctime(localtime(&timer)));
 
    char buffer[MAX_SOURCE_LINE];
    int line_number = 0;
    int page_number = 0;
    int line_count  = LINES_PER_PAGE;
 
    while (fgets(buffer, MAX_SOURCE_LINE, file) != NULL) {
        buffer[strcspn(buffer, "\r\n")] = '\0'; // remove newline
 
        ++line_number;
 
        if (++line_count > LINES_PER_PAGE) {
            printf("\fPage %d   %s   %s\n\n",
               ++page_number, source_name, date);
            line_count = 1;
        }
 
        char *out = buffer;
        int len = strlen(buffer);
 
        if (len == 0) {
            printf("%4d:\n", line_number);
            continue;
        }
 
        while (len > 0) {
            char save_ch = '\0';
            if (len > MAX_PRINT_LINE) {
                save_ch = out[MAX_PRINT_LINE];
                out[MAX_PRINT_LINE] = '\0';
            }
 
            if (out == buffer)
                printf("%4d: %s\n", line_number, out);
            else
                printf("      %s\n", out);
 
            if (len < MAX_PRINT_LINE)
                len = 0;
            else {
                out[MAX_PRINT_LINE] = save_ch;
                out += MAX_PRINT_LINE;
                len -= MAX_PRINT_LINE;
            }
        }
    }
 
    return 0;
}

Prototypes are only necessary in C source code for forward declaration purposes only.

If you arrange code in bottom up order (main is last), you only ever need a prototype for weird mutual recursion cases.

But having all the prototypes at the start of the source file anyway is a useful documentation overview of what's in the rest of the file.

Because FILE is properly declared in stdio.h, and is the standard type name to hold information about files opened within the program.

How much C do you know?

Taking 30+ year old C from pre-ANSI days and trying to drag it into the 21st century is a "cleaning the Augean stables" type task.

Lastly, copy/paste the raw text from your IDE.
Fuzzy pictures are useless to refer to or comment on.

For example, the fgets() in the first picture is referring to a file handle that no longer? exists.

Post a link to a zipfile of all the code in the project on a site like: file.io - Super simple file sharing

Is this from 1991, Ronald Mak, Writing Compilers and Interpreters, 3rd edition?

Is this even supposed to compile?
I get about 6 errors and 200 warnings.
I notice in the top comment of calc.c:
/* see compiler2.c chapter 14 for extern FILE fix! */
And in the top comment of scanner.c
/* line 75 col 47 [Error] expected expression before 'FILE' */

FILE has been used as an enum constant, which seems kind of idiotic.
Maybe you should change the enum to FILE2.

EDIT: This basically compiles: https://file.io/oaKiSk5HQXOS