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21 | |
| 22 | <span style="float:right">systemd 221</span><hr><div class="refentry"><a name="sd_journal_next"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_journal_next, sd_journal_previous, sd_journal_next_skip, sd_journal_previous_skip, SD_JOURNAL_FOREACH, SD_JOURNAL_FOREACH_BACKWARDS — Advance or set back the read pointer in the journal</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-journal.h></pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_next</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_previous</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_next_skip</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>uint64_t <var class="pdparam">skip</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_previous_skip</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>uint64_t <var class="pdparam">skip</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef"><b class="fsfunc">SD_JOURNAL_FOREACH</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef"><b class="fsfunc">SD_JOURNAL_FOREACH_BACKWARDS</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm47952643779984"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_journal_next()</code> advances the read | |
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23 | pointer into the journal by one entry. The only argument taken is |
| 24 | a journal context object as allocated via | |
| 25 | <a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>. | |
| 26 | After successful invocation the entry may be read with functions | |
| 27 | such as | |
| 28 | <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>.</p><p>Similarly, <code class="function">sd_journal_previous()</code> sets | |
| 29 | the read pointer back one entry.</p><p><code class="function">sd_journal_next_skip()</code> and | |
| 30 | <code class="function">sd_journal_previous_skip()</code> advance/set back | |
| 31 | the read pointer by multiple entries at once, as specified in the | |
| 32 | <code class="varname">skip</code> parameter.</p><p>The journal is strictly ordered by reception time, and hence | |
| 33 | advancing to the next entry guarantees that the entry then | |
| 34 | pointing to is later in time than then previous one, or has the | |
| 35 | same timestamp.</p><p>Note that | |
| 36 | <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a> | |
| 37 | and related calls will fail unless | |
| 38 | <code class="function">sd_journal_next()</code> has been invoked at least | |
| 39 | once in order to position the read pointer on a journal | |
| 40 | entry.</p><p>Note that the <code class="function">SD_JOURNAL_FOREACH()</code> | |
| 41 | macro may be used as a wrapper around | |
| 42 | <a href="sd_journal_seek_head.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_seek_head</span>(3)</span></a> | |
| 43 | and <code class="function">sd_journal_next()</code> in order to make | |
| 44 | iterating through the journal easier. See below for an example. | |
| 45 | Similarly, <code class="function">SD_JOURNAL_FOREACH_BACKWARDS()</code> may | |
| 86f210e9 | 46 | be used for iterating the journal in reverse order.</p></div><div class="refsect1"><a name="idm47952643768000"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p>The four calls return the number of entries advanced/set |
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47 | back on success or a negative errno-style error code. When the end |
| 48 | or beginning of the journal is reached, a number smaller than | |
| 49 | requested is returned. More specifically, if | |
| 50 | <code class="function">sd_journal_next()</code> or | |
| 51 | <code class="function">sd_journal_previous()</code> reach the end/beginning | |
| 52 | of the journal they will return 0, instead of 1 when they are | |
| 86f210e9 | 53 | successful. This should be considered an EOF marker.</p></div><div class="refsect1"><a name="idm47952643765184"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p>The <code class="function">sd_journal_next()</code>, |
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54 | <code class="function">sd_journal_previous()</code>, |
| 55 | <code class="function">sd_journal_next_skip()</code> and | |
| 56 | <code class="function">sd_journal_previous_skip()</code> interfaces are | |
| 57 | available as a shared library, which can be compiled and linked to | |
| 58 | with the | |
| 59 | <code class="constant">libsystemd</code> <a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a> | |
| 86f210e9 | 60 | file.</p></div><div class="refsect1"><a name="idm47952643760016"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>Iterating through the journal:</p><pre class="programlisting">#include <stdio.h> |
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61 | #include <string.h> |
| 62 | #include <systemd/sd-journal.h> | |
| 63 | ||
| 64 | int main(int argc, char *argv[]) { | |
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65 | int r; |
| 66 | sd_journal *j; | |
| 67 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
| 68 | if (r < 0) { | |
| 69 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
| 70 | return 1; | |
| 71 | } | |
| 72 | SD_JOURNAL_FOREACH(j) { | |
| 73 | const char *d; | |
| 74 | size_t l; | |
| 663996b3 | 75 | |
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76 | r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l); |
| 77 | if (r < 0) { | |
| 78 | fprintf(stderr, "Failed to read message field: %s\n", strerror(-r)); | |
| 79 | continue; | |
| 80 | } | |
| 663996b3 | 81 | |
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82 | printf("%.*s\n", (int) l, d); |
| 83 | } | |
| 84 | sd_journal_close(j); | |
| 85 | return 0; | |
| 86f210e9 | 86 | }</pre></div><div class="refsect1"><a name="idm47952643757392"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p> |
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87 | <a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>, |
| 88 | <a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>, | |
| 89 | <a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>, | |
| 90 | <a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>, | |
| 91 | <a href="sd_journal_get_realtime_usec.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_realtime_usec</span>(3)</span></a>, | |
| 92 | <a href="sd_journal_get_cursor.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_cursor</span>(3)</span></a> | |
| 93 | </p></div></div></body></html> |