Add new format_to_string function

This simply writes values formatted with format_rec to a string and returns that
instead of an ostream, which is useful if immediate output isn’t the desired
behaviour.

Author: hannes-steffenhagen-diffblue

src/util/format.h

@@ -10,6 +10,8 @@ Author: Daniel Kroening, kroening@kroening.com
 #define CPROVER_UTIL_FORMAT_H
 
 #include <iosfwd>
+#include <sstream>
+#include <string>
 
 //! The below enables convenient syntax for feeding
 //! objects into streams, via stream << format(o)
@@ -37,4 +39,12 @@ static inline format_containert<T> format(const T &o)
   return format_containert<T>(o);
 }
 
+template <typename T>
+std::string format_to_string(const T &o)
+{
+  std::ostringstream oss;
+  oss << format(o);
+  return oss.str();
+}
+
 #endif // CPROVER_UTIL_FORMAT_H