Add nasm_strdupto() and nasm_strto(), to replace a string variable

It is common enough that one wants to set a string pointer to a newly
allocated string, freeing the old one if it is not NULL.

Add specific helper functions for this.

Signed-off-by: H. Peter Anvin (Intel) <hpa@zytor.com>

include/nasmlib.h

@@ -102,6 +102,29 @@ char * safe_alloc nasm_strndup(const char *, size_t);
 char * safe_alloc nasm_strcat(const char *one, const char *two);
 char * safe_alloc end_with_null nasm_strcatn(const char *one, ...);
 
+/*
+ * Replace a string in a string pointer variable with a nasm_strdup()
+ * copy of the argument on the right, freeing the contents of the
+ * previous contents of the variable if non-NULL.
+ *
+ * If *str is NULL, simply return the old value of *ptrp.
+ */
+char *nasm_strdupto(char **ptrp, const char *str);
+
+/*
+ * Similar, but the new pointer must already have been heap allocated
+ * by the creating function.
+ */
+static inline char *nasm_strto(char **ptrp, char *str)
+{
+    char *ptr = *ptrp;
+    if (!str)
+        return ptr;
+    if (ptr)
+        nasm_free(ptr);
+    return *ptrp = str;
+}
+
 /*
  * nasm_[v]asprintf() are variants of the semi-standard [v]asprintf()
  * functions, except that we return the pointer instead of a count.

nasmlib/alloc.c

@@ -99,6 +99,17 @@ char *nasm_strndup(const char *s, size_t len)
     return memcpy(p, s, len);
 }
 
+char *nasm_strdupto(char **ptrp, const char *str)
+{
+    char *ptr = *ptrp;
+    if (str) {
+        if (ptr)
+            nasm_free(ptr);
+        *ptrp = ptr = nasm_strdup(str);
+    }
+    return ptr;
+}
+
 char *nasm_strcat(const char *one, const char *two)
 {
     char *rslt;