#LyX 2.0 created this file. For more info see http://www.lyx.org/
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\end_header

\begin_body

\begin_layout Title
LyX and Literate Programming
\begin_inset Newline newline
\end_inset

An example program
\end_layout

\begin_layout Author
Edmar Wienskoski Jr.
\begin_inset Newline newline
\end_inset

edmar-w-jr@technologist.com
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
Modified by Bernard Michael Hurley bernardh@westherts.ac.uk ---- Don't blame
 Edmar for any errors that have crept in!
\end_layout

\end_inset


\end_layout

\begin_layout Abstract

\series bold
Note:
\series default
 This example program is provided for educational use only.
 The functionality in this C program has been superceded by the equivalent
 Python code in 
\emph on
examples/listerrors.lyx
\emph default
 which should be installed in the LyX scripts directory.
\end_layout

\begin_layout Date
\begin_inset ERT
status collapsed

\begin_layout Plain Layout


\backslash
today
\end_layout

\end_inset


\end_layout

\begin_layout Standard
\begin_inset CommandInset toc
LatexCommand tableofcontents

\end_inset


\end_layout

\begin_layout Section
Introduction
\end_layout

\begin_layout Standard
After typesetting a document, LyX scans the LaTeX log file looking for errors.
 For each error found, the line number is obtained and a error box is displayed
 in the LyX screen at that position.
\end_layout

\begin_layout Standard
To use this feature to view compilation errors while working with literate
 documents, we need a program that filters the compilation errors and puts
 them in a format suitable for LyX reading it.
 
\end_layout

\begin_layout Standard
In this document we present a filter that recognizes compilation error messages
 from noweb, gnu C, and the IBM C compiler (xlc).
\end_layout

\begin_layout Standard
The filter is required to read from standard input, parse for error messages
 and copy the error messages to the standard output.
 During the output process, the filter must present the error messages in
 a format that LyX can interpret, currently, the LaTeX error message format.
 Of course, nothing will prevent future LyX releases from being able to
 read other formats as well (like gcc error messages for example).
 This mechanism is necessary to fully explore the literate programming tool's
 capabilities.
\end_layout

\begin_layout Section
Algorithm
\end_layout

\begin_layout Scrap
<<Function bodies>>=
\end_layout

\begin_layout Scrap
int
\end_layout

\begin_layout Scrap
main (int argc, char **argv)
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  if (argc == 2) {
\end_layout

\begin_layout Scrap
    switch (argv[1][0]) {
\end_layout

\begin_layout Scrap
    case 'n':
\end_layout

\begin_layout Scrap
      <<Scan input for noweb error messages>>
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    case 'x':
\end_layout

\begin_layout Scrap
      <<Scan input for xlc error messages>>
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    case 'a':
\end_layout

\begin_layout Scrap
      <<AIX system using both noweb and xlc>>
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    case 's':
\end_layout

\begin_layout Scrap
    case 'b':
\end_layout

\begin_layout Scrap
      <<Solaris and Linux systems using both noweb and gcc>>
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    case 'g':
\end_layout

\begin_layout Scrap
    default:
\end_layout

\begin_layout Scrap
      <<Scan input for gcc error messages>>
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    }
\end_layout

\begin_layout Scrap
  } else {
\end_layout

\begin_layout Scrap
    <<Scan input for gcc error messages>>
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Scrap
<<Function prototypes>>=
\end_layout

\begin_layout Scrap
int main (int argc, char **argv);
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Section
Data Structures
\end_layout

\begin_layout Standard
We resort to some global variables to allow access from several different
 routines.
 These are the buffer and related pointers used during the parse of the
 input.
\end_layout

\begin_layout Scrap
<<Global variables>>=
\end_layout

\begin_layout Scrap
char    buffer[200][200];
\begin_inset Newline newline
\end_inset

int     last_buf_line;
\begin_inset Newline newline
\end_inset

int     last_err_line;
\begin_inset Newline newline
\end_inset

int     err_line;
\begin_inset Newline newline
\end_inset

@ 
\end_layout

\begin_layout Section
The output format
\end_layout

\begin_layout Standard
The output format mimics the TeX error messages format.
 This function prints a number of lines residing in the global variable
 
\family typewriter
buffer
\family default
, a program name and line number.
 There is no special requirement on the input strings, they can be anything.
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
This function has been slightly changed from EW's original to make scanning
 a bit easier with LaTeX::scanLogFile().
 The test has been added because LyX can crash if empty lines are allowed
 here --- I can't figure out why! --- BMH
\end_layout

\end_inset


\end_layout

\begin_layout Scrap
<<Function bodies>>=
\end_layout

\begin_layout Scrap
void
\end_layout

\begin_layout Scrap
output_error (int buf_size, int error_line, char *tool)
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  int     i;
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
  fprintf(stdout, "! Build Error: ==> %s ==>
\backslash
n", tool);
\end_layout

\begin_layout Scrap
  fprintf(stdout, " ...
\backslash
n
\backslash
nl.%d ...
\backslash
n", error_line);
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
  for (i=0; i<buf_size; i++)
\end_layout

\begin_layout Scrap
    if (strlen(buffer[i]) != 0)
\end_layout

\begin_layout Scrap
      fprintf(stdout, "%s", buffer[i]);
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
  fprintf(stdout, "
\backslash
n");
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Scrap
<<Function prototypes>>=
\end_layout

\begin_layout Scrap
void output_error (int buf_size, int error_line, char *tool);
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Section
Functions Implementation
\end_layout

\begin_layout Standard
Both noweave and notangle routines, always output one single line for each
 error found, thus to scan the buffer for noweb error messages is enough
 to exam one input line at a time.
 Note that the noweb software does not provide a line error number, so all
 errors boxes related to noweb messages will be displayed at the beginning
 of the file.
\end_layout

\begin_layout Scrap
<<Scan input for noweb error messages>>=
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  last_buf_line = 0;
\end_layout

\begin_layout Scrap
  while (fgets(buffer[0], 200, stdin)) {
\end_layout

\begin_layout Scrap
    if (noweb_try(0))
\end_layout

\begin_layout Scrap
      output_error(1, err_line, "noweb");
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
The examination itself is very inefficient.
 Unfortunately noweb doesn't have any characteristic that would help to
 identify one of its error messages.
 The solution is to collect all possible output messages in an array of
 strings, and turn the examination process into a linear search in this
 array.
\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap
<<Global variables>>=
\end_layout

\begin_layout Scrap
char *noweb_msgs[] = {
\end_layout

\begin_layout Scrap
  "couldn't open file",
\end_layout

\begin_layout Scrap
  "couldn't open temporary file",
\end_layout

\begin_layout Scrap
  "error writing temporary file",
\end_layout

\begin_layout Scrap
  "ill-formed option",
\end_layout

\begin_layout Scrap
  "unknown option",
\end_layout

\begin_layout Scrap
  "Bad format sequence",
\end_layout

\begin_layout Scrap
  "Can't open output file",
\end_layout

\begin_layout Scrap
  "Can't open temporary file",
\end_layout

\begin_layout Scrap
  "Capacity exceeded:",
\end_layout

\begin_layout Scrap
  "Ignoring unknown option -",
\end_layout

\begin_layout Scrap
  "This can't happen:",
\end_layout

\begin_layout Scrap
  "non-numeric line number in"
\end_layout

\begin_layout Scrap
};
\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap
char *noweb_msgs_mimic_gcc[] = {
\end_layout

\begin_layout Scrap
  ": unescaped << in documentation chunk"
\end_layout

\begin_layout Scrap
};
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
A noweb error message can be any string that contains a matching pair of
 < <
\begin_inset space ~
\end_inset


\begin_inset space ~
\end_inset


\begin_inset space ~
\end_inset

> >, or any of the above strings
\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap
<<Function bodies>>=
\begin_inset Newline newline
\end_inset

int
\begin_inset Newline newline
\end_inset

noweb_try (int buf_line)
\begin_inset Newline newline
\end_inset

{
\begin_inset Newline newline
\end_inset

  char    *s, *t, *b;
\begin_inset Newline newline
\end_inset

  int     i; 
\begin_inset Newline newline
\end_inset


\begin_inset Newline newline
\end_inset

  b = buffer[buf_line];
\begin_inset Newline newline
\end_inset

  err_line = 0;
\begin_inset Newline newline
\end_inset


\begin_inset Newline newline
\end_inset

  for (i=0; i<1; i++) {
\begin_inset Newline newline
\end_inset

      s = (char *)strstr (b, noweb_msgs_mimic_gcc[i]);
\begin_inset Newline newline
\end_inset

      if (s != NULL) {
\begin_inset Newline newline
\end_inset

        t = (char *)strchr(buffer[buf_line], ':');
\begin_inset Newline newline
\end_inset

        err_line = atoi(t+1);
\begin_inset Newline newline
\end_inset

        t = buffer[buf_line];
\begin_inset Newline newline
\end_inset

        ++s;
\begin_inset Newline newline
\end_inset

        while (*(t++) = *(s++));
\begin_inset Newline newline
\end_inset

        return 1;
\begin_inset Newline newline
\end_inset

      }
\begin_inset Newline newline
\end_inset

  }
\begin_inset Newline newline
\end_inset

  s = (char *)strstr(b, "<<");
\begin_inset Newline newline
\end_inset

  if (s != NULL) {
\begin_inset Newline newline
\end_inset

    s = (char *)strstr(s+2, ">>");
\begin_inset Newline newline
\end_inset

    if (s != NULL) {
\begin_inset Newline newline
\end_inset

      return 1;
\begin_inset Newline newline
\end_inset

    }
\begin_inset Newline newline
\end_inset

  } else { 
\begin_inset Newline newline
\end_inset

     for (i = 0; i < 12; ++i) {
\begin_inset Newline newline
\end_inset

        s = (char *)strstr (b, noweb_msgs[i]);
\begin_inset Newline newline
\end_inset

        if (s != NULL) {
\begin_inset Newline newline
\end_inset

           return 1;
\begin_inset Newline newline
\end_inset

        }
\begin_inset Newline newline
\end_inset

    }
\begin_inset Newline newline
\end_inset

  }
\begin_inset Newline newline
\end_inset

  return 0;
\begin_inset Newline newline
\end_inset

}
\begin_inset Newline newline
\end_inset

@
\end_layout

\begin_layout Scrap
<<Function prototypes>>=
\end_layout

\begin_layout Scrap
int noweb_try (int buf_line);
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
The xlc compiler always outputs one single line for each error found, thus
 to scan the buffer for xlc error messages it is enough to exam one input
 line at a time.
\end_layout

\begin_layout Scrap
<<Scan input for xlc error messages>>= 
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  last_buf_line = 0;
\end_layout

\begin_layout Scrap
  while (fgets(buffer[last_buf_line], 200, stdin)) {
\end_layout

\begin_layout Scrap
    if (xlc_try(0))
\end_layout

\begin_layout Scrap
      output_error(1, err_line, "xlc");
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
A xlc error message is easy to identify.
 Every error message starts with a quoted string with no spaces, a comma,
 a space, the word 
\begin_inset Quotes eld
\end_inset

line
\begin_inset Quotes erd
\end_inset

, a space, and some variable text.
 The following routine tests if a given buffer line matches this criteria:
\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap
<<Function bodies>>=
\end_layout

\begin_layout Scrap
int 
\end_layout

\begin_layout Scrap
xlc_try (int buf_line)
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  char    *s, *t;
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
  t = buffer[buf_line];
\end_layout

\begin_layout Scrap
  s = t+1;
\end_layout

\begin_layout Scrap
  while (*s != '"' && *s != ' ' && *s != '
\backslash
0')
\end_layout

\begin_layout Scrap
    s++;
\end_layout

\begin_layout Scrap
  if (*t != '"' || *s != '"' || strncmp(s+1, ", line ", 7) != 0)
\end_layout

\begin_layout Scrap
    return 0;
\end_layout

\begin_layout Scrap
  s += 8;
\end_layout

\begin_layout Scrap
  err_line = atoi(s);
\end_layout

\begin_layout Scrap
  return 1;
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Scrap
<<Function prototypes>>=
\end_layout

\begin_layout Scrap
int xlc_try (int buf_line);
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
The gcc compiler error messages are more complicated to scan.
 Each error can span more than one line in the buffer.
 The good news is that every buffer line on each error has the same pattern,
 and share the same line number.
 Thus the strategy will be to accumulate lines in the buffer while the reported
 line number is still the same.
 At the time they differ, all the accumulated lines, except the last one,
 will belong to one single error message, which now can be output-ed to
 LyX.
\end_layout

\begin_layout Standard
Every gcc error message contains a string with no space followed by a 
\begin_inset Quotes eld
\end_inset

:
\begin_inset Quotes eld
\end_inset

.
 If the next character is a space, then this line is a header of a error
 message and the next line will detail the line number of the source code
 where the error was found.
 Otherwise, the next thing is a integer number followed by another 
\begin_inset Quotes eld
\end_inset

:
\begin_inset Quotes eld
\end_inset

.
\end_layout

\begin_layout Scrap
<<Scan input for gcc error messages>>=
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  char    *s, *t;
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
  last_buf_line = 0;
\end_layout

\begin_layout Scrap
  while (fgets(buffer[last_buf_line], 200, stdin)) {
\end_layout

\begin_layout Scrap
    /****** Skip lines until I find an error */
\end_layout

\begin_layout Scrap
    s = (char *)strpbrk(buffer[last_buf_line], " :");
\end_layout

\begin_layout Scrap
    if (s == NULL || *s == ' ')
\end_layout

\begin_layout Scrap
      continue; /* No gcc error found here */
\end_layout

\begin_layout Scrap
    do {
\end_layout

\begin_layout Scrap
      <<gcc error message criteria is to find a "...:999:" or a "...: ">>
\end_layout

\begin_layout Scrap
      /****** OK It is an error message, get line number */
\end_layout

\begin_layout Scrap
      err_line = atoi(s+1);
\end_layout

\begin_layout Scrap
      if (last_err_line == 0 || last_err_line == err_line) {
\end_layout

\begin_layout Scrap
        last_err_line = err_line;
\end_layout

\begin_layout Scrap
        continue; /* It's either a header or a continuation, don't output
 yet */
\end_layout

\begin_layout Scrap
      }
\end_layout

\begin_layout Scrap
      /****** Completed the scan of one error message, output it to LyX
 */
\end_layout

\begin_layout Scrap
      discharge_buffer(1);
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    } while (fgets(buffer[last_buf_line], 200, stdin));
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
  /****** EOF completes the scan of whatever was being scanned */
\end_layout

\begin_layout Scrap
  discharge_buffer(0);
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Scrap
<<gcc error message criteria is to find a "...:999:" or a "...: ">>=
\end_layout

\begin_layout Scrap
/****** Search first ":" in the error number */
\end_layout

\begin_layout Scrap
s = (char *)strpbrk(buffer[last_buf_line], " :");
\end_layout

\begin_layout Scrap
last_buf_line++;
\end_layout

\begin_layout Scrap
if (s == NULL || *s == ' ') 
\end_layout

\begin_layout Scrap
  <<No gcc error found here, but it might terminate the scanning of a previous
 one>>
\end_layout

\begin_layout Scrap
/****** Search second ":" in the error number */
\end_layout

\begin_layout Scrap
t = (char *)strpbrk(s+1, " :");
\begin_inset Newline newline
\end_inset

if (t == NULL || *t == ' ')
\begin_inset Newline newline
\end_inset

  <<No gcc error found here, but it might terminate the scanning of a previous
 one>>
\begin_inset Newline newline
\end_inset

/****** Verify if is all digits between ":" */
\begin_inset Newline newline
\end_inset

if (t != s+1+strspn(s+1, "0123456789")) 
\begin_inset Newline newline
\end_inset

  <<No gcc error found here, but it might terminate the scanning of a previous
 one>>
\begin_inset Newline newline
\end_inset

@
\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap
<<No gcc error found here, but it might terminate the scanning of a previous
 one>>=
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  err_line = 0;
\end_layout

\begin_layout Scrap
  discharge_buffer(1);
\end_layout

\begin_layout Scrap
  continue;
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
As we mentioned, when the scan of one gcc error message is completed everything
 in the buffer except the last line is one single error message.
 But if the scan terminates with a EOF or through finding one line that
 does not match the gcc error message criteria, then there is no 
\begin_inset Quotes eld
\end_inset

last line
\begin_inset Quotes erd
\end_inset

 in the buffer to be concerned with.
 In those cases we empty the buffer completely.
\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap

\end_layout

\begin_layout Scrap
<<Function bodies>>=
\end_layout

\begin_layout Scrap
void
\end_layout

\begin_layout Scrap
discharge_buffer (int save_last)
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
 if (last_err_line != 0) { 
\end_layout

\begin_layout Scrap
   clean_gcc_messages();
\end_layout

\begin_layout Scrap
   if (save_last != 0) {
\end_layout

\begin_layout Scrap
      output_error(last_buf_line-1, last_err_line, "gcc");
\end_layout

\begin_layout Scrap
      strcpy (buffer[0], buffer[last_buf_line-1]);
\end_layout

\begin_layout Scrap
      last_err_line = err_line;
\end_layout

\begin_layout Scrap
      last_buf_line = 1;
\end_layout

\begin_layout Scrap
    } else { 
\end_layout

\begin_layout Scrap
      ++last_buf_line;
\end_layout

\begin_layout Scrap
      clean_gcc_messages();
\end_layout

\begin_layout Scrap
      output_error(last_buf_line-1, last_err_line, "gcc");
\end_layout

\begin_layout Scrap
      last_err_line = 0;
\end_layout

\begin_layout Scrap
      last_buf_line = 0;
\end_layout

\begin_layout Scrap
    }
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Scrap
<<Function prototypes>>=
\end_layout

\begin_layout Scrap
void discharge_buffer (int save_last);
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
The next function 
\begin_inset Quotes eld
\end_inset

cleans
\begin_inset Quotes erd
\end_inset

 superfluous information from gcc messages, namely the name of the noweb
 file and the line number of the Error.
\begin_inset Foot
status collapsed

\begin_layout Plain Layout
More could be done.
 For instance, some way of distinguishing between gcc Errors and Warnings
 should be devised.
\end_layout

\end_inset


\end_layout

\begin_layout Scrap
<<Function bodies>>=
\end_layout

\begin_layout Scrap
void
\end_layout

\begin_layout Scrap
clean_gcc_messages ()
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  int index;
\end_layout

\begin_layout Scrap
  char search [30]; 
\end_layout

\begin_layout Scrap
  char *tail, *head; 
\end_layout

\begin_layout Scrap
  int search_len = sprintf(search, ".nw:%d:", last_err_line);
\end_layout

\begin_layout Scrap
  
\end_layout

\begin_layout Scrap
  for (index = 0; index < last_buf_line-1; index++) {
\end_layout

\begin_layout Scrap
    tail = (char *)strstr (buffer[index], search);
\end_layout

\begin_layout Scrap
    if ( tail == NULL) {
\end_layout

\begin_layout Scrap
       tail = (char *) strstr (buffer[index], ".nw:");
\end_layout

\begin_layout Scrap
       if (tail) {
\end_layout

\begin_layout Scrap
          tail += 4;
\end_layout

\begin_layout Scrap
       }
\end_layout

\begin_layout Scrap
    } else {
\end_layout

\begin_layout Scrap
       tail += search_len;
\end_layout

\begin_layout Scrap
    }
\end_layout

\begin_layout Scrap
    if (tail != NULL) {
\end_layout

\begin_layout Scrap
       head = buffer[index];
\end_layout

\begin_layout Scrap
       while (*(head++) = *(tail++));
\end_layout

\begin_layout Scrap
    }
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Scrap
<<Function prototypes>>=
\end_layout

\begin_layout Scrap
void clean_gcc_messages ();
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
To combine the scan of noweb error messages and xlc error messages is very
 simple.
 We just try each one for every input line:
\end_layout

\begin_layout Scrap
<<AIX system using both noweb and xlc>>=
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  last_buf_line = 0;
\begin_inset Newline newline
\end_inset

  while (fgets(buffer[0], 200, stdin)) {
\begin_inset Newline newline
\end_inset

    if (noweb_try(0))
\begin_inset Newline newline
\end_inset

      output_error(1, err_line, "noweb");
\begin_inset Newline newline
\end_inset

    else if (xlc_try(0))
\begin_inset Newline newline
\end_inset

      output_error(1, err_line, "xlc");
\begin_inset Newline newline
\end_inset

  }
\begin_inset Newline newline
\end_inset

}
\begin_inset Newline newline
\end_inset

@
\end_layout

\begin_layout Standard
To combine the scan of noweb error messages and gcc error messages is simple
 if we realize that it is not possible to find a noweb error message in
 the middle of a gcc error message.
 So we just repeat the gcc procedure and test for noweb error messages in
 the beginning of the scan:
\end_layout

\begin_layout Scrap
<<Solaris and Linux systems using both noweb and gcc>>=
\end_layout

\begin_layout Scrap
{
\end_layout

\begin_layout Scrap
  char    *s, *t;
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
  last_buf_line = 0;
\end_layout

\begin_layout Scrap
  while (fgets(buffer[last_buf_line], 200, stdin)) {
\end_layout

\begin_layout Scrap
    /****** Skip lines until I find an error */
\end_layout

\begin_layout Scrap
    if (last_buf_line == 0 && noweb_try(0)) {
\end_layout

\begin_layout Scrap
      output_error(1, err_line, "noweb");
\end_layout

\begin_layout Scrap
      continue;
\end_layout

\begin_layout Scrap
    }
\end_layout

\begin_layout Scrap
    s = (char *)strpbrk(buffer[last_buf_line], " :");
\end_layout

\begin_layout Scrap
    if (s == NULL || *s == ' ')
\end_layout

\begin_layout Scrap
      continue; /* No gcc error found here */
\end_layout

\begin_layout Scrap
    do {
\end_layout

\begin_layout Scrap
      <<gcc error message criteria is to find a "...:999:" or a "...: ">>
\end_layout

\begin_layout Scrap
      /****** OK It is an error, get line number */
\end_layout

\begin_layout Scrap
      err_line = atoi(s+1);
\end_layout

\begin_layout Scrap
      if (last_err_line == 0 || last_err_line == err_line) {
\end_layout

\begin_layout Scrap
        last_err_line = err_line;
\end_layout

\begin_layout Scrap
        continue; /* It's either a header or a continuation, don't output
 yet */
\end_layout

\begin_layout Scrap
      }
\end_layout

\begin_layout Scrap
      /****** Completed the scan of one error message, output it to LyX
 */
\end_layout

\begin_layout Scrap
      discharge_buffer(1);
\end_layout

\begin_layout Scrap
      break;
\end_layout

\begin_layout Scrap
    } while (fgets(buffer[last_buf_line], 200, stdin));
\end_layout

\begin_layout Scrap
  }
\end_layout

\begin_layout Scrap
  /****** EOF completes the scan of whatever was being scanned */
\end_layout

\begin_layout Scrap
  discharge_buffer(0);
\end_layout

\begin_layout Scrap
}
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Section
Wrapping the code into a file
\end_layout

\begin_layout Scrap
<<listerrors.c>>=
\end_layout

\begin_layout Scrap
#include <stdio.h>
\end_layout

\begin_layout Scrap
#include <strings.h>       
\end_layout

\begin_layout Scrap
 
\end_layout

\begin_layout Scrap
<<Global variables>>
\end_layout

\begin_layout Scrap
<<Function prototypes>>
\end_layout

\begin_layout Scrap
<<Function bodies>>
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
To build this program, we want to add the 
\begin_inset Quotes eld
\end_inset

-L
\begin_inset Quotes erd
\end_inset

 option in the tangle command to force gdb to load the file 
\family typewriter
Literate.nw
\family default
 instead of 
\family typewriter
listerrors.c
\family default
.
 In accordance with this, we pass the 
\begin_inset Quotes eld
\end_inset

-g
\begin_inset Quotes erd
\end_inset

 option to gcc.
\end_layout

\begin_layout Scrap
<<build-script>>=
\end_layout

\begin_layout Scrap
#!/bin/sh
\end_layout

\begin_layout Scrap
if [ -z "$NOWEB_SOURCE" ]; then NOWEB_SOURCE=Literate.nw; fi
\end_layout

\begin_layout Scrap
notangle -L -Rlisterrors.c ${NOWEB_SOURCE} > listerrors.c
\end_layout

\begin_layout Scrap
gcc -g -o listerrors listerrors.c
\end_layout

\begin_layout Scrap
@
\end_layout

\begin_layout Standard
This project can be tangled and compiled from LyX if you set 
\family typewriter

\backslash
build_command
\family default
 to call a generic script that always extracts a scrap named 
\family typewriter
build-script
\family default
 and executes it.
 Here is a example of such generic script:
\end_layout

\begin_layout LyX-Code
#!/bin/sh
\begin_inset Newline newline
\end_inset

notangle -Rbuild-script $1 | env NOWEB_SOURCE=$1 sh
\end_layout

\begin_layout LyX-Code

\end_layout

\end_body
\end_document
