Add support for fopenf(), formatted string fopen()

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

README.md

@@ -181,6 +181,15 @@ Generic Functions
 
   Check for the existence of a directory, returns True(1) or False(0).
 
+- `fopenf(mode, fmt, ...)`
+
+  Like `fopen()`, but takes a formatted string as argument.  This
+  greatly simplifies operations that usually consist of composing a
+  filename from parts into a dynamic buffer before actually opening
+  the file.
+  
+  > **Notice:** the swapped order of `pathname` and `mode`!
+
 - `fsendfile(src, dst, len)`
 
   Copy data between file streams, very similar to `fcopyfile()`, but

src/Makefile.am

@@ -5,7 +5,7 @@ libite_la_CFLAGS      = -W -Wall -Wextra
 libite_la_LDFLAGS     = $(AM_LDFLAGS) -version-info 5:1:0
 libite_la_SOURCES     = chomp.c		copyfile.c			\
 			conio.c		conio.h				\
-			dir.c						\
+			dir.c		fopenf.c			\
 			fexist.c	fisdir.c			\
 			fparseln.c	fsendfile.c			\
 			ifconfig.c	lfile.c				\

src/fopenf.c

@@ -0,0 +1,61 @@
+/* Formatted fopen()
+ *
+ * Copyright (c) 2020  Joachim Nilsson <troglobit@gmail.com>
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <stdio.h>
+#include <stdarg.h>
+#include <stdlib.h>
+
+/**
+ * fopenf - Open a file based on the formatted string and optional arguments
+ * @mode: Last argument in optional list, if omitted EINVAL
+ * @fmt:  Formatted string to be composed into a pathname
+ *
+ * This function is an extension to the fopen() family, lessening the burden
+ * of first having to compose the filename from parts in a seprate buffer.
+ *
+ * Returns:
+ * Upon successful completion fopenf() a FILE pointer.  Otherwise, NULL
+ * is returned and errno is set to indicate the error.
+ */
+FILE *fopenf(const char *mode, const char *fmt, ...)
+{
+	va_list ap;
+	FILE *fp = NULL;
+	char *file;
+	int len;
+
+	va_start(ap, fmt);
+	len = vsnprintf(NULL, 0, fmt, ap);
+	va_end(ap);
+
+	va_start(ap, fmt);
+	file = alloca(len + 1);
+	if (file) {
+		vsnprintf(file, len + 1, fmt, ap);
+		fp = fopen(file, mode);
+	}
+	va_end(ap);
+
+	return fp;
+}
+
+/**
+ * Local Variables:
+ *  indent-tabs-mode: t
+ *  c-file-style: "linux"
+ * End:
+ */

src/lite.h

@@ -65,6 +65,7 @@ char   *fparseln   (FILE *, size_t *, size_t *, const char[3], int);
 int     fexist     (const char *file);
 int     fisdir     (const char *path);
 
+FILE   *fopenf     (const char *mode, const char *fmt, ...);
 FILE   *tempfile   (void);
 ssize_t copyfile   (const char *src, const char *dst, int len, int opt);
 int     movefile   (const char *src, const char *dst);

tests/.gitignore

@@ -1,11 +1,13 @@
 *.o
 *.log
 *.trs
+.deps/
 chomp
 copyfile
 dir
 fexist
 fisdir
+fopenf
 fsendfile
 lfile
 makepath

tests/Makefile.am

@@ -7,6 +7,7 @@ TESTS          += copyfile
 TESTS          += dir
 TESTS          += fexist
 TESTS          += fisdir
+TESTS          += fopenf
 TESTS          += fsendfile
 TESTS          += lfile
 TESTS          += makepath

tests/fopenf.c

@@ -0,0 +1,18 @@
+#include "check.h"
+
+int main(void)
+{
+	FILE *fp;
+	char *dir = "/tmp";
+	char *file = "__foo__";
+
+	fp = fopenf("w", "%s/%s", dir, file);
+	if (fp) {
+		fputs("foo", fp);
+		fclose(fp);
+	}
+
+	fail_unless(fexist("/tmp/__foo__"));
+
+	return 0;
+}