ctrace(1) (Advanced C Utilities) ctrace(1)
NAME
ctrace - C program debugger
SYNOPSIS
ctrace [options] [file]
DESCRIPTION
The ctrace command allows the user to monitor the sequential
execution of a C program as each program statement executes. 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 the
user does 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.
The output of ctrace must be placed into a temporary file because the
cc(1) command does not allow the use of a pipe. This file can then
be compiled and executed.
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; these variable names and values will be
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 after each 1000 loop cycles to help the
user detect infinite loops. The trace output goes to the standard
output so the user 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.
The user 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. The
user 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:
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ctrace(1) (Advanced C Utilities) ctrace(1)
-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.
-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 Preprocess the input before tracing it. The user can also use
the -D, -I, and -U cc(1) options.
-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 replacement lets the user change the entire print
function, instead of just the name and leading arguments (see
the -p option).
-V Prints version information on the standard error.
-Qarg If arg is y, identification information about ctrace will be
added to the output files. This can be useful for software
administration. Giving n for arg exlicitly asks for no such
information, which is the default behavior.
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 }
these commands and test data are entered:
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 incorrect because there is only one
line in the test data. The error in this program is common, but
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ctrace(1) (Advanced C Utilities) ctrace(1)
subtle. If the user invokes ctrace with these commands:
ctrace lc.c >temp.c
cc temp.c
a.out
the output will be:
2 main()
6 nl = 0;
/* nl == 0 */
7 while ((c = getchar()) != EOF)
The program is now waiting for input. If the user enters 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 an end-of-file character (cntl-d) is entered, the final output
will be:
/* c == -1 */
10 printf("%d\n", nl);
/* nl == 2 */2
return
Note the information printed out at the end of the trace line for the
nl variable following line 10. 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 user attention is
drawn to this if statement, he or she will probably realize that the
assignment operator (=) was used in place of the equality operator
(==). This error can easily be missed during code reading.
EXECUTION-TIME TRACE CONTROL
The default operation for ctrace is to trace the entire program file,
unless the -f or -v options are used to trace specific functions.
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ctrace(1) (Advanced C Utilities) ctrace(1)
The default operation does not give the user statement-by-statement
control of the tracing, nor does it let the user turn the tracing off
and on when executing the traced program.
The user can do both of these by adding ctroff() and ctron() function
calls to the program to turn the tracing off and on, respectively, at
execution time. Thus, complex criteria can be arbitrarily coded for
trace control with if statements, and this code can even be
conditionally included because ctrace defines the CTRACE preprocessor
variable. For example:
#ifdef CTRACE
if (c == '!' && i > 1000)
ctron();
#endif
These functions can also be called from sdb(1) if they are compiled
with the -g option. For example, to trace all but lines 7 to 10 in
the main function, enter:
sdb a.out
main:7b ctroff()
main:11b ctron()
r
The trace can be turned off and on by setting static variable trct
to 0 and 1, respectively. This on/off option is useful if a user is
using a debugger that can not call these functions directly.
DIAGNOSTICS
This section contains diagnostic messages from both ctrace and cc(1),
since the traced code often gets some cc warning messages. The user
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
tabs are used to indent the 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.
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ctrace(1) (Advanced C Utilities) ctrace(1)
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.
SEE ALSO
sdb(1), ctype(3C), fclose(3S), printf(3S), string(3C).
bfs(1), tail(1) in the User's Reference Manual.
NOTES
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.
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. Separate output elimination 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/ccs/lib/ctrace/runtime.c run-time trace package
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