ctang-output.ch

Changes for CTANGLE.W by Andreas Scherer, October 2021.

This set of changes modifies the output behaviour of the CWEB system.
Instead of writing directly to the C or TeX file as described in the
manual, the current run is documented in a temporary output file which is
copied to the expected file in the last moment.  In case of an user abort,
previous results are not destroyed.

This change file requires CTANG-PATCH.CH to be applied as well.

For a complete history of the changes made to CTANGLE.W see CTANG-PATCH.CH.

Section 50.

@x l.556
@<Write all the named output files@>=
for (an_output_file=end_output_files; an_output_file>cur_out_file;) {
    an_output_file--;
    sprint_section_name(output_file_name,*an_output_file);
    fclose(C_file);
    if ((C_file=fopen(output_file_name,"wb"))==NULL)
      fatal("! Cannot open output file ",output_file_name);
@.Cannot open output file@>
    if (show_progress) { printf("\n(%s)",output_file_name); update_terminal(); }
    cur_line=1;
    @<Initialize the secondary output@>@;
    @<Output material...@>@;
}
@y
@<Write all the named output files@>=
if (check_for_change) {
  fclose(C_file); C_file=NULL;
  @<Update the primary result when it has changed@>@;
}
for (an_output_file=end_output_files; an_output_file>cur_out_file;) {
  an_output_file--;
  sprint_section_name(output_file_name,*an_output_file);
  if (check_for_change) @<Open the intermediate output file@>@;
  else {
    fclose(C_file);
    if ((C_file=fopen(output_file_name,"wb"))==NULL)
      fatal("! Cannot open output file ",output_file_name);
@.Cannot open output file@>
  }
  if (show_progress) { printf("\n(%s)",output_file_name); update_terminal(); }
  cur_line=1;
  @<Initialize the secondary output@>@;
  @<Output material...@>@;
  if (check_for_change) {
    fclose(C_file); C_file=NULL;
    @<Update the secondary results when they have changed@>@;
  }
}
if (check_for_change)
  strcpy(check_file_name,""); /* We want to get rid of the temporary file */
@z

Additional material.

@x l.1551
@** Index.
@y
@* Output file update. Most \CEE/ projects are controlled by a \.{Makefile}
that automatically takes care of the temporal dependencies between the different
source modules. It may be convenient that \.{CWEB} doesn't create new output
for all existing files, when there are only changes to some of them. Thus the
\.{make} process will only recompile those modules where necessary. You can
activate this feature with the `\.{+c}' command-line option. The idea and basic
implementation of this mechanism can be found in the program \.{NUWEB} by
Preston Briggs, to whom credit is due.

@<Open the intermediate output file@>= {
  if ((C_file=fopen(output_file_name,"a"))==NULL)
    fatal("! Cannot open output file ",output_file_name);
@.Cannot open output file@>
  else fclose(C_file); /* Test accessability */
  if((C_file=fopen(check_file_name,"wb"))==NULL)
    fatal("! Cannot open output file ",check_file_name);
}

@ @<Update the primary result...@>=
if((C_file=fopen(C_file_name,"r"))!=NULL) {
  @<Set up the comparison of temporary output@>@;
  @<Create the primary output depending on the comparison@>@;
} else
  rename(check_file_name,C_file_name); /* This was the first run */

@ @<Set up the comparison of temporary output@>=
  bool comparison=false;

  if((check_file=fopen(check_file_name,"r"))==NULL)
    fatal("! Cannot open output file ",check_file_name);
@.Cannot open output file@>

  @<Compare the temporary output...@>@;

  fclose(C_file); C_file=NULL;
  fclose(check_file); check_file=NULL;

@ We hope that this runs fast on most systems.

@<Compare the temporary output to the previous output@>=
do {
  char x[BUFSIZ],y[BUFSIZ];
  int x_size = fread(x,sizeof(char),BUFSIZ,C_file);
  int y_size = fread(y,sizeof(char),BUFSIZ,check_file);
  comparison = (x_size == y_size) && !memcmp(x,y,x_size);
} while(comparison && !feof(C_file) && !feof(check_file));

@ Note the superfluous call to |remove| before |rename|.  We're using it to
get around a bug in some implementations of |rename|.@^system dependencies@>

@<Create the primary output...@>=
if(comparison)
  remove(check_file_name); /* The output remains untouched */
else {
  remove(C_file_name);
  rename(check_file_name,C_file_name);
}

@ The author of a \.{CWEB} program may want to write the \\{secondary} output
instead of to a file (in \.{@@(...@@>}) to \.{/dev/null} or \.{/dev/stdout} or
\.{/dev/stderr}.  We must take care of the \\{temporary} output already written
to a file and finally get rid of that file.

@<Update the secondary results...@>=
if(0==strcmp("/dev/stdout",output_file_name))@/
  @<Redirect temporary output to \.{/dev/stdout}@>@;
else if(0==strcmp("/dev/stderr",output_file_name))@/
  @<Redirect temporary output to \.{/dev/stderr}@>@;
else if(0==strcmp("/dev/null",output_file_name))@/
  @<Redirect temporary output to \.{/dev/null}@>@;
else { /* Hopefully a regular output file */
  if((C_file=fopen(output_file_name,"r"))!=NULL) {
    @<Set up the comparison of temporary output@>@;
    @<Create the secondary output depending on the comparison@>@;
  } else
    rename(check_file_name,output_file_name); /* This was the first run */
}

@ Again, we use a call to |remove| before |rename|.

@<Create the secondary output...@>=
if(comparison)
  remove(check_file_name); /* The output remains untouched */
else {
  remove(output_file_name);
  rename(check_file_name,output_file_name);
}

@ Copy secondary output to |stdout|.

@<Redirect temporary output to \.{/dev/stdout}@>={
  @<Setup system redirection@>@;
  do {
    in_size = fread(in_buf,sizeof(char),BUFSIZ,check_file);
    in_buf[in_size]='\0';
    fprintf(stdout,"%s",in_buf);
  } while(!feof(check_file));@/
  fclose(check_file); check_file=NULL;
  @<Create the secondary output...@>@;
}

@ Copy secondary output to |stderr|.

@<Redirect temporary output to \.{/dev/stderr}@>={
  @<Setup system redirection@>@;
  do {
    in_size = fread(in_buf,sizeof(char),BUFSIZ,check_file);
    in_buf[in_size]='\0';
    fprintf(stderr,"%s",in_buf);
  } while(!feof(check_file));@/
  fclose(check_file); check_file=NULL;
  @<Create the secondary output...@>@;
}

@ No copying necessary, just remove the temporary output file.

@<Redirect temporary output to \.{/dev/null}@>={
  bool comparison=true;
  @<Create the secondary output...@>@;
}

@ @<Setup system redirection@>=
char in_buf[BUFSIZ+1];
int in_size;
bool comparison=true;
if((check_file=fopen(check_file_name,"r"))==NULL)
  fatal("! Cannot open output file ",check_file_name);
@.Cannot open output file@>

@** Index.
@z