# libtraceevent(3) Manual Page

## NAME

trace_seq_init, trace_seq_destroy, trace_seq_reset, trace_seq_terminate, trace_seq_putc, trace_seq_puts, trace_seq_printf, trace_seq_vprintf, trace_seq_do_fprintf, trace_seq_do_printf - Initialize / destroy a trace sequence.

## SYNOPSIS

    #include <event-parse.h>
    #include <trace-seq.h>

    void trace_seq_init(struct trace_seq *s);
    void trace_seq_destroy(struct trace_seq *s);
    void trace_seq_reset(struct trace_seq *s);
    void trace_seq_terminate(struct trace_seq *s);
    int trace_seq_putc(struct trace_seq *s, unsigned char c);
    int trace_seq_puts(struct trace_seq *s, const char *str);
    int trace_seq_printf(struct trace_seq *s, const char *fmt, …);
    int trace_seq_vprintf(struct trace_seq *s, const char *fmt, va_list args);
    int trace_seq_do_printf(struct trace_seq *s);
    int trace_seq_do_fprintf(struct trace_seq *s, FILE *fp);

## DESCRIPTION

Trace sequences are used to allow a function to call several other functions to create a string of data to use.

The trace_seq_init() function initializes the trace sequence s.

The trace_seq_destroy() function destroys the trace sequence s and frees all its resources that it had used.

The trace_seq_reset() function re-initializes the trace sequence s. All characters already written in s will be deleted.

The trace_seq_terminate() function terminates the trace sequence s. It puts the null character '\0' at the end of the buffer.

The trace_seq_putc() function puts a single character c in the trace sequence s.

The trace_seq_puts() function puts a NULL terminated string str in the trace sequence s.

The trace_seq_printf() function puts a formated string fmt _with variable arguments _… in the trace sequence s.

The trace_seq_vprintf() function puts a formated string fmt _with list of arguments _args in the trace sequence s.

The trace_seq_do_printf() function prints the buffer of trace sequence s to the standard output stdout.

The trace_seq_do_fprintf() function prints the buffer of trace sequence s to the given file fp.

## RETURN VALUE

Both trace_seq_putc() and trace_seq_puts() functions return the number of characters put in the trace sequence, or 0 in case of an error

Both trace_seq_printf() and trace_seq_vprintf() functions return 0 if the trace oversizes the buffer’s free space, the number of characters printed, or a negative value in case of an error.

Both trace_seq_do_printf() and trace_seq_do_fprintf() functions return the number of printed characters, or -1 in case of an error.

## EXAMPLE

    #include <event-parse.h>
    #include <trace-seq.h>
    ...
    struct trace_seq seq;
    trace_seq_init(&seq);
    ...
    void foo_seq_print(struct trace_seq *tseq, char *format, ...)
    {
            va_list ap;
            va_start(ap, format);
            if (trace_seq_vprintf(tseq, format, ap) <= 0) {
                    /* Failed to print in the trace sequence */
            }
            va_end(ap);
    }

    trace_seq_reset(&seq);

    char *str = " MAN page example";
    if (trace_seq_puts(&seq, str) != strlen(str)) {
            /* Failed to put str in the trace sequence */
    }
    if (trace_seq_putc(&seq, ':') != 1) {
            /* Failed to put ':' in the trace sequence */
    }
    if (trace_seq_printf(&seq, " trace sequence: %d", 1) <= 0) {
            /* Failed to print in the trace sequence */
    }
    foo_seq_print( &seq, "  %d\n", 2);

    trace_seq_terminate(&seq);
    ...

    if (trace_seq_do_printf(&seq) < 0 ) {
            /* Failed to print the sequence buffer to the standard output */
    }
    FILE *fp = fopen("trace.txt", "w");
    if (trace_seq_do_fprintf(&seq, fp) < 0 ) [
            /* Failed to print the sequence buffer to the trace.txt file */
    }

    trace_seq_destroy(&seq);
    ...

## FILES

    event-parse.h
            Header file to include in order to have access to the library APIs.
    trace-seq.h
            Header file to include in order to have access to trace sequences related APIs.
    -ltraceevent
            Linker switch to add when building a program that uses the library.

## SEE ALSO

libtraceevent(3), trace-cmd(1)

## AUTHOR

    Steven Rostedt <rostedt@goodmis.org>, author of libtraceevent.
    Tzvetomir Stoyanov <tz.stoyanov@gmail.com>, author of this man page.

## REPORTING BUGS

Report bugs to <linux-trace-devel@vger.kernel.org>

## LICENSE

libtraceevent is Free Software licensed under the GNU LGPL 2.1

## RESOURCES

https://git.kernel.org/pub/scm/libs/libtrace/libtraceevent.git/