Add examples for output capture (fixes #691)

1 files changed, 100 insertions, 0 deletions

diff --git a/examples/qpdfjob-c-save-attachment.c b/examples/qpdfjob-c-save-attachment.c
new file mode 100644
index 00000000..950e297b
--- /dev/null
+++ b/examples/qpdfjob-c-save-attachment.c
@@ -0,0 +1,100 @@
+#include <qpdf/Constants.h>
+#include <qpdf/qpdfjob-c.h>
+#include <qpdf/qpdflogger-c.h>
+
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+
+// This example demonstrates how we can redirect where saved output
+// goes by calling the default logger's setSave method before running
+// something with QPDFJob. See qpdfjob-c-save-attachment.c for an
+// implementation that uses the C API.
+
+static void
+save_to_file(char const* data, size_t len, void* udata)
+{
+    FILE* f = (FILE*)udata;
+    fwrite(data, 1, len, f);
+}
+
+static FILE*
+do_fopen(char const* filename)
+{
+    FILE* f = NULL;
+#ifdef _MSC_VER
+    if (fopen_s(&f, filename, "wb") != 0) {
+        f = NULL;
+    }
+#else
+    f = fopen(filename, "wb");
+#endif
+    if (f == NULL) {
+        fprintf(stderr, "unable to open %s\n", filename);
+        exit(2);
+    }
+    return f;
+}
+
+int
+main(int argc, char* argv[])
+{
+    char const* whoami = "qpdfjob-c-save-attachment";
+    char const* filename = NULL;
+    char const* key = NULL;
+    char const* outfilename = NULL;
+    char* attachment_arg = NULL;
+    char const* attachment_flag = "--show-attachment=";
+    size_t flag_len = 0;
+    FILE* outfile = NULL;
+    int status = 0;
+    qpdfjob_handle j = NULL;
+    qpdflogger_handle l = qpdflogger_default_logger();
+
+    if (argc != 4) {
+        fprintf(stderr, "Usage: %s file attachment-key outfile\n", whoami);
+        exit(2);
+    }
+
+    filename = argv[1];
+    key = argv[2];
+    outfilename = argv[3];
+
+    flag_len = strlen(attachment_flag) + strlen(key) + 1;
+    attachment_arg = malloc(flag_len);
+#ifdef _MSC_VER
+    strncpy_s(attachment_arg, flag_len, attachment_flag, flag_len);
+    strncat_s(attachment_arg, flag_len, key, flag_len - strlen(attachment_arg));
+#else
+    strncpy(attachment_arg, attachment_flag, flag_len);
+    strncat(attachment_arg, key, flag_len - strlen(attachment_arg));
+#endif
+
+    char const* j_argv[5] = {
+        whoami,
+        filename,
+        attachment_arg,
+        "--",
+        NULL,
+    };
+    outfile = do_fopen(outfilename);
+
+    /* Use qpdflogger_set_save with a callback function to redirect
+     * saved data. You can use other qpdf logger functions to capture
+     * informational output, warnings, and errors.
+     */
+    qpdflogger_set_save(
+        l, qpdf_log_dest_custom, save_to_file, (void*)outfile, 0);
+    qpdflogger_cleanup(&l);
+    j = qpdfjob_init();
+    status = (qpdfjob_initialize_from_argv(j, j_argv) ||
+              qpdfjob_run(j));
+    qpdfjob_cleanup(&j);
+    free(attachment_arg);
+    fclose(outfile);
+    if (status == qpdf_exit_success) {
+        printf("%s: wrote attachment to %s\n", whoami, outfilename);
+    }
+    return 0;
+}