Tracing Execution

Tracing collects information about what is happening in your program and displays it. If a program arrives at a breakpoint created with a trace command, the program halts and an event-specific trace information line is emitted, then the program continues.

A trace displays each line of source code as it is about to be executed. In all but the simplest programs, this trace produces volumes of output.

A more useful trace applies a filter to display information about events in your program. For example, you can trace each call to a function, every member function of a given name, every function in a class, or each exit from a function. You can also trace changes to a variable.

Setting a Trace

Set a trace by typing a trace command at the command line. The basic syntax of the trace command is:

trace event-specification [ modifier ]

For the complete syntax of the trace command, see trace Command.

The information a trace provides depends on the type of event associated with it (see Setting Event Specifications).

Controlling the Speed of a Trace

Often trace output goes by too quickly. The dbx environment variable trace_speed lets you control the delay after each trace is printed. The default delay is 0.5 seconds.

To set the interval in seconds between execution of each line of code during a trace, type:

dbxenv trace_speed number

Directing Trace Output to a File

You can direct the output of a trace to a file using the -file filename option. For example, the following command direct trace output to the file trace1:

(dbx) trace -file trace1

To revert trace output to standard output use - for filename. Trace output is always appended to filename. It is flushed whenever dbx prompts and when the application has exited. The filename is always re-opened on a new run or resumption after an attach.