Add beginsWith helper to rdcinflexiblestr

renderdoc/api/replay/rdcstr.h

@@ -1121,6 +1121,42 @@ public:
   bool empty() const { return c_str()[0] == 0; }
   const char *c_str() const { return (const char *)(uintptr_t)pointer; }
   size_t size() const { return strlen(c_str()); }
+  bool beginsWith(const char *beginning) const
+  {
+    if(!beginning)
+      return false;
+
+    const char *a = c_str();
+    const char *b = beginning;
+
+    // empty string we're checking against, degenerate case but true
+    if(*b == 0)
+      return true;
+
+    // if we are an empty string we don't match any non-empty prefix
+    if(*a == 0)
+      return false;
+
+    while(*a && *b)
+    {
+      if(*a != *b)
+        return false;
+
+      a++;
+      b++;
+
+      // if we reached the end of beginning before hitting a difference, we do begin with it
+      if(*b == 0)
+        return true;
+
+      // if we reached the end of our own string but beginning still has something left, we don't begin with it
+      if(*a == 0)
+        return false;
+    }
+
+    // should never reach here
+    return false;
+  }
   operator rdcstr() const
   {
     if(is_literal == 0)

renderdoc/replay/basic_types_tests.cpp

@@ -2112,6 +2112,12 @@ TEST_CASE("Test string type", "[basictypes][string]")
     CHECK_FALSE(test == rdcinflexiblestr("Hello, World!"));
     CHECK_FALSE(test.empty());
 
+    CHECK(test.beginsWith("Hello"));
+    CHECK(test.beginsWith(""));
+    CHECK_FALSE(test.beginsWith(NULL));
+    CHECK_FALSE(test.beginsWith("Hello!"));
+    CHECK_FALSE(test.beginsWith("Hello, World!!"));
+
     rdcstr str = test;
 
     CHECK(str == "Hello, World");