add asprintf

core/klibc.c

@@ -1,3 +1,4 @@
+#include "alloc.h"
 #include "klibc.h"
 #include "serial.h"
 #include "vga.h"
@@ -211,7 +212,7 @@ int vsnprintf(char *str, size_t size, const char *format, va_list ap)
     int i   = 0;
     int c   = 0;
 
-    while (format[i] != '\0' && size) {
+    while (format[i] != '\0' && (size|| !str)) {
         switch (format[i]) {
             case '%':
                 switch (format[i + 1]) {
@@ -381,3 +382,47 @@ int vprintf(const char *fmt, va_list ap)
     }
     return ret;
 }
+
+int asprintf(char **strp, const char *fmt, ...)
+{
+    int ret;
+
+    va_list ap;
+    va_start(ap, fmt);
+    ret = vasprintf(strp, fmt, ap);
+    va_end(ap);
+
+    return ret;
+}
+
+int vasprintf(char **strp, const char *fmt, va_list ap)
+{
+    int n       = 0;
+    size_t size = 0;
+    char *p     = NULL;
+
+    /* Determine required size */
+
+    n = vsnprintf(p, size, fmt, ap);
+	printf("Found length %d\n", n);
+
+    if (n < 0)
+        return -1;
+
+    /* One extra byte for '\0' */
+
+    size = (size_t)n + 1;
+    p    = malloc(size);
+    if (p == NULL)
+        return -1;
+
+    n = vsnprintf(p, size, fmt, ap);
+
+    if (n < 0) {
+        free(p);
+        return -1;
+    }
+	*strp = p;
+
+    return size;
+}

core/klibc.h

@@ -25,6 +25,10 @@ int vsnprintf(char *str, size_t size, const char *format, va_list ap);
 int vprintf(const char *format, va_list ap);
 int printf(const char *format, ...);
 
+// Could be used after malloc is available
+int asprintf(char **strp, const char *fmt, ...);
+int vasprintf(char **strp, const char *fmt, va_list ap);
+
 /*
  * Dummy printk for disabled debugging statements to use whilst maintaining
  * gcc's format checking.

tests/test.c

@@ -312,6 +312,7 @@ void testKthread()
 
 void run_test(void)
 {
+    {
         int test             = 1000;
         long long int test64 = 0x100000000;
         assert(printf("hello") == 5);
@@ -320,6 +321,14 @@ void run_test(void)
         assert(printf("hello %llx\n", test64) == 16);
         assert(printf("hello %c\n", 'a') == 8);
         assert(printf("hello %s\n", "world") == 12);
+    }
+    {
+        char *strAlloc;
+        int ret = asprintf(&strAlloc, "hello %s\n", "world");
+        printf("asprint ret %d %s\n", ret, strAlloc);
+        assert(ret == 13); //include the '\0'
+        free(strAlloc);
+    }
     testPaging();
     printf("Testing Serial\n");
     serialPutc('h');