regex.3: Add example program

$ gcc -Wall -Wextra -Werror -pedantic regex.c -o regex
$ ./regex.3
String = "1) John Driverhacker;
2) John Doe;
3) John Foo;
"
Matches:
#0:
offset = 25; length = 7
substring = "John Do"
#1:
offset = 38; length = 8
substring = "John Foo"

Signed-off-by: Alejandro Colomar <colomar.6.4.3@gmail.com>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

diff --git a/man3/regex.3 b/man3/regex.3
index 7c5132995036e7883502c122b13f78d405f863b6..3144c2ceb1ac2eac7d04dd58e126da921cb937f8 100644 (file)
--- a/man3/regex.3
+++ b/man3/regex.3
@@ -337,6 +337,48 @@ T} Thread safety   MT-Safe
 .TE
 .SH CONFORMING TO
 POSIX.1-2001, POSIX.1-2008.
+.SH EXAMPLES
+.EX
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <regex.h>
+
+#define ARRAY_SIZE(arr) (sizeof((arr)) / sizeof((arr)[0]))
+
+static const char *const str =
+        "1) John Driverhacker;\en2) John Doe;\en3) John Foo;\en";
+static const char *const re = "John.*o";
+
+int main(void)
+{
+    static const char *s = str;
+    regex_t     regex;
+    regmatch_t  pmatch[1];
+    regoff_t    off, len;
+
+    if (regcomp(&regex, re, REG_NEWLINE))
+        exit(EXIT_FAILURE);
+
+    printf("String = \e"%s\e"\en", str);
+    printf("Matches:\en");
+
+    for (int i = 0; ; i++) {
+        if (regexec(&regex, s, ARRAY_SIZE(pmatch), pmatch, 0))
+            break;
+
+        off = pmatch[0].rm_so + (s \- str);
+        len = pmatch[0].rm_eo \- pmatch[0].rm_so;
+        printf("#%d:\en", i);
+        printf("offset = %jd; length = %jd\en", (intmax_t) off, (intmax_t) len);
+        printf("substring = \e"%.*s\e"\en", len, s + pmatch[0].rm_so);
+
+        s += pmatch[0].rm_eo;
+    }
+
+    exit(EXIT_SUCCESS);
+}
+.EE
 .SH SEE ALSO
 .BR grep (1),
 .BR regex (7)