strbuf: strbuf_append_va

docs/technical/strbuf.txt

@@ -43,6 +43,26 @@ Functions
 
     Adds the formated-string 'fmt' to the end of ->buf.
 
+`strbuf_append_va()`::
+
+    Adds the formated-string 'fmt' (generated by a `va_list`) to the end of ->buf. +
+    Returns the number of characters that should have been written if ->buf was large enough. +
+    Therefor if the function returns zero. all characters has been written. +
+    +
+    Example usage:
++
+----
+va_start(va, fmt);
+len = strbuf_append_va(s, fmt, va);
+va_end(va);
+
+if (len > 0) {
+    strbuf_expand(s, len);
+    va_start(va, fmt);
+    len = strbuf_append_va(s, fmt, va);
+    va_end(va);
+}
+----
 `strbuf_append_str()`::
 
     Will add the 'str' C-string to the end of ->buf

src/strbuf.c

@@ -122,28 +122,34 @@ void strbuf_append(strbuf_t *s, const void *ptr, size_t len) {
 
 void strbuf_appendf(strbuf_t *s, const char *fmt, ...) {
 
-    va_list vl;
+    va_list va;
     int len;
-
+    
     if (!strbuf_avail(s))
         strbuf_expand(s, CHNK_SIZE-1);
 
-    va_start(vl, fmt);
-    len = vsnprintf(s->buf + s->len, s->alloc_size - s->len, fmt, vl);
-    va_end(vl);
+    va_start(va, fmt);
+    len = strbuf_append_va(s, fmt, va);
+    va_end(va);
 
+    if (len > 0) {
+    	strbuf_expand(s, len);
+    	va_start(va, fmt);
+    	len = strbuf_append_va(s, fmt, va);
+    	va_end(va);
+    }
+}
+
+int strbuf_append_va(strbuf_t *s, const char *fmt, va_list va) {
+
+    int len = vsnprintf(s->buf + s->len, s->alloc_size - s->len, fmt, va);
     if (len < 0)
         die_errno("vsnprintf");
-    if (len > strbuf_avail(s)) {
-        strbuf_expand(s, len);
-        va_start(vl, fmt);
-        len = vsnprintf(s->buf + s->len, s->alloc_size - s->len, fmt, vl);
-        va_end(vl);
-        if (len > strbuf_avail(s))
-            die_errno("vsnprintf");
-    }
+    if (len > strbuf_avail(s))
+        return len;
     s->len += len;
     s->buf[len] = '\0';
+    return 0;
 }
 
 void strbuf_append_str(strbuf_t *s, const char *str) {

src/strbuf.h

@@ -12,6 +12,7 @@
 #define __STRBUF_H
 
 #include <stddef.h>
+#include <stdarg.h>
 
 typedef struct {
     size_t alloc_size;
@@ -45,6 +46,8 @@ void strbuf_append(strbuf_t *s, const void *ptr, size_t len);
 
 void strbuf_appendf(strbuf_t *s, const char *fmt, ...);
 
+int strbuf_append_va(strbuf_t *s, const char *fmt, va_list va);
+
 void strbuf_append_str(strbuf_t *s, const char *str);
 
 void strbuf_append_ch(strbuf_t *s, char ch);