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CTRACE(1)		       Silicon Graphics			     CTRACE(1)

NAME
     ctrace - C program debugger

SYNOPSIS
     ctrace [options] [file]

DESCRIPTION
     The ctrace command allows you to follow the execution  of	a  C  program,
     statement-by-statement.   The  effect  is	similar	 to  executing a shell
     procedure with the -x option.  ctrace reads the C	program	 in  file  (or
     from  standard  input  if you do not specify file), inserts statements to
     print the text of	each  executable  statement  and  the  values  of  all
     variables	referenced or modified, and writes the modified program to the
     standard output.  You must put the output of ctrace into a temporary file
     because  the  cc(1)  command  does not allow the use of a pipe.  You then
     compile and execute this file.

     As each statement in the program  executes	 it  will  be  listed  at  the
     terminal,	followed  by the name and value of any variables referenced or
     modified in the statement, followed by any	 output	 from  the  statement.
     Loops  in	the trace output are detected and tracing is stopped until the
     loop is exited or a different sequence of statements within the  loop  is
     executed.	A warning message is printed every 1000 times through the loop
     to help you detect infinite loops.	 The trace output goes to the standard
     output  so	 you  can put it into a file for examination with an editor or
     the bfs(1) or tail(1) commands.

     The options commonly used are:

     -f functions  Trace only these functions.
     -v functions  Trace all but these functions.

     You may want to add to the default formats for printing variables.	  Long
     and pointer variables are always printed as signed integers.  Pointers to
     character arrays are also	printed	 as  strings  if  appropriate.	 Char,
     short,  and  int  variables  are  also printed as signed integers and, if
     appropriate, as characters.  Double variables  are	 printed  as  floating
     point  numbers in scientific notation.  You can request that variables be
     printed in additional formats, if appropriate, with these options:

     -o	    Octal
     -x	    Hexadecimal
     -u	    Unsigned
     -e	    Floating point

     These options are used only in special circumstances:

     -l n   Check  n  consecutively  executed  statements  for	looping	 trace
	    output,  instead of the default of 20.  Use 0 to get all the trace
	    output from loops.

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CTRACE(1)		       Silicon Graphics			     CTRACE(1)

     -s	    Suppress redundant trace output from simple assignment  statements
	    and string copy function calls.  This option can hide a bug caused
	    by use of the = operator in place of the == operator.
     -t n   Trace n variables per statement instead of the default of 10  (the
	    maximum  number  is 20).  The Diagnostics section explains when to
	    use this option.
     -P	    Run the C preprocessor on the input before tracing	it.   You  can
	    also use the -D, -I, and -U cpp(1) options.

     These options are used to tailor the  run-time  trace  package  when  the
     traced program will run in a non-UNIX System environment:

     -b	    Use only basic functions in the trace  code,  that	is,  those  in
	    ctype(3C),	 printf(3S),   and   string(3C).   These  are  usually
	    available  even  in	 cross-compilers  for	microprocessors.    In
	    particular,	 this  option  is  needed when the traced program runs
	    under  an  operating  system  that	does   not   have   signal(2),
	    fflush(3S), longjmp(3C), or setjmp(3C).
     -p string
	    Change the trace print function from  the  default	of  'printf('.
	    For	 example,  'fprintf(stderr,'  would  send  the	trace  to  the
	    standard error output.
     -r f   Use file f in place of the runtime.c trace function package.  This
	    lets  you  change  the  entire print function, instead of just the
	    name and leading arguments (see the -p option).

EXAMPLE
     If the file lc.c contains this C program:

	   1 #include <stdio.h>
	   2 main() /* count lines in input */
	   3 {
	   4   int c, nl;
	   5
	   6   nl = 0;
	   7   while ((c = getchar()) != EOF)
	   8	    if (c = '\n')
	   9		 ++nl;
	  10   printf("%d\n", nl);
	  11 }
     and you enter these commands and test data:
	  cc lc.c
	  a.out
	  1
	  (cntl-d)
     the program will be compiled and executed.	 The output of the program
     will be the number 2, which is not correct because there is only one line
     in the test data.	The error in this program is common, but subtle.  If
     you invoke ctrace with these commands:
	  ctrace lc.c >temp.c
	  cc temp.c
	  a.out

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CTRACE(1)		       Silicon Graphics			     CTRACE(1)

     the output will be:
	   2 main()
	   6   nl = 0;
	       /* nl == 0 */
	   7   while ((c = getchar()) != EOF)
     The program is now waiting for input.  If you enter the same test data as
     before, the output will be:
	       /* c == 49 or '1' */
	   8	    if (c = '\n')
		    /* c == 10 or '\n' */
	   9		 ++nl;
			 /* nl == 1 */
	   7   while ((c = getchar()) != EOF)
	       /* c == 10 or '\n' */
	   8	    if (c = '\n')
		    /* c == 10 or '\n' */
	   9		 ++nl;
			 /* nl == 2 */
	   7   while ((c = getchar()) != EOF)
     If you now enter an end of file character (cntl-d) the final output will
     be:
	       /* c == -1 */
	  10   printf("%d\n", nl);
	       /* nl == 2 */2
		return
     Note that the program output printed at the end of the trace line for the
     nl variable.  Also note the return comment added by ctrace at the end of
     the trace output.	This shows the implicit return at the terminating
     brace in the function.

     The trace output shows that variable c is assigned the value '1' in line
     7, but in line 8 it has the value '\n'.  Once your attention is drawn to
     this if statement, you will probably realize that you used the assignment
     operator (=) in place of the equality operator (==).  You can easily miss
     this error during code reading.

EXECUTION-TIME TRACE CONTROL
     The default operation for ctrace is to trace the entire program file,
     unless you use the -f or -v options to trace specific functions.  This
     does not give you statement-by-statement control of the tracing, nor does
     it let you turn the tracing off and on when executing the traced program.

     You can do both of these by adding ctroff() and ctron() function calls to
     your program to turn the tracing off and on, respectively, at execution
     time.  Thus, you can code arbitrarily complex criteria for trace control
     with if statements, and you can even conditionally include this code
     because ctrace defines the CTRACE preprocessor variable.  For example:

	  #ifdef CTRACE
	       if (c == '!' && i > 1000)
		    ctron();
	  #endif

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CTRACE(1)		       Silicon Graphics			     CTRACE(1)

     You can also control tracing from dbx(1) if you compile with the -g
     option by turning trace on and off with the static variable tr_ct_..  For
     example, to trace all but lines 7 to 10 in the main function, enter:

	  dbx a.out
	  when at 7 { assign tr_ct_ = 0 }
	  when at 11 { assign tr_ct_ = 1 }
	  run

DIAGNOSTICS
     This section contains diagnostic messages from both ctrace and cc(1),
     since the traced code often gets some cc warning messages.	 You can get
     cc error messages in some rare cases, all of which can be avoided.

   ctrace Diagnostics
     warning: some variables are not traced in this statement
	  Only 10 variables are traced in a statement to prevent the C
	  compiler "out of tree space; simplify expression" error.  Use the -t
	  option to increase this number.

     warning: statement too long to trace
	  This statement is over 400 characters long.  Make sure that you are
	  using tabs to indent your code, not spaces.

     cannot handle preprocessor code, use -P option
	  This is usually caused by #ifdef/#endif preprocessor statements in
	  the middle of a C statement, or by a semicolon at the end of a
	  #define preprocessor statement.

     'if ... else if' sequence too long
	  Split the sequence by removing an else from the middle.

     possible syntax error, try -P option
	  Use the -P option to preprocess the ctrace input, along with any
	  appropriate -D, -I, and -U preprocessor options.  If you still get
	  the error message, check the Warnings section below.

   Cc Diagnostics
     warning: illegal combination of pointer and integer
     warning: statement not reached
     warning: sizeof returns 0
	  Ignore these messages.

     compiler takes size of function
	  See the ctrace "possible syntax error" message above.

     yacc stack overflow
	  See the ctrace "'if ... else if' sequence too long" message above.

Page 4				 Release 6.4

CTRACE(1)		       Silicon Graphics			     CTRACE(1)

     out of tree space; simplify expression
	  Use the -t option to reduce the number of traced variables per
	  statement from the default of 10.  Ignore the "ctrace: too many
	  variables to trace" warnings you will now get.

     redeclaration of signal
	  Either correct this declaration of signal(2), or remove it and
	  #include <signal.h>.

SEE ALSO
     bfs(1), dbx(1), tail(1), signal(2), ctype(3C), fclose(3S), printf(3S),
     setjmp(3C), string(3C).

WARNINGS
     You will get a ctrace syntax error if you omit the semicolon at the end
     of the last element declaration in a structure or union, just before the
     right brace (}).  This is optional in some C compilers.

     Defining a function with the same name as a system function may cause a
     syntax error if the number of arguments is changed.  Just use a different
     name.

     ctrace assumes that BADMAG is a preprocessor macro, and that EOF and NULL
     are #defined constants.  Declaring any of these to be variables, e.g.,
     "int EOF;", will cause a syntax error.

BUGS
     ctrace does not know about the components of aggregates like structures,
     unions, and arrays.  It cannot choose a format to print all the
     components of an aggregate when an assignment is made to the entire
     aggregate.	 ctrace may choose to print the address of an aggregate or use
     the wrong format (e.g., 3.149050e-311 for a structure with two integer
     members) when printing the value of an aggregate.

     Pointer values are always treated as pointers to character strings.

     The loop trace output elimination is done separately for each file of a
     multi-file program.  This can result in functions called from a loop
     still being traced, or the elimination of trace output from one function
     in a file until another in the same file is called.

FILES
     /usr/lib/ctrace/runtime.c		run-time trace package

Page 5				 Release 6.4

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