helper to escape while printing strings

src/factory/printer.cpp

@@ -5,6 +5,7 @@
  */
 
 #include <stdio.h>
+#include <ctype.h>
 #if defined(__linux__) || defined(__APPLE__)
 #include <unistd.h>
 #define HAVE_ISATTY
@@ -13,6 +14,7 @@
 #include <deque>
 
 #include <epicsTime.h>
+#include <epicsString.h>
 
 #define epicsExportSharedSymbols
 #include <pv/bitSet.h>
@@ -436,4 +438,57 @@ std::ostream& operator<<(std::ostream& strm, const PVStructure::Formatter& forma
     return strm;
 }
 
+static char hexdigit(char c) {
+    c &= 0xf;
+    if(c<9)
+        return '0'+c;
+    else
+        return 'A'+c-10;
+}
+
+escape::~escape() {}
+
+std::string escape::str() const
+{
+    std::ostringstream strm;
+    strm<<(*this);
+    return strm.str();
+}
+
+epicsShareFunc
+std::ostream& operator<<(std::ostream& strm, const escape& Q)
+{
+    for(size_t pos = 0, len = Q.orig.size(); pos < len; pos++) {
+        const char C = Q.orig[pos];
+        char quote = '\\', next;
+        // compare me with epicsStrnEscapedFromRaw()
+        switch(C) {
+        case '\a': next = 'a'; break;
+        case '\b': next = 'b'; break;
+        case '\f': next = 'f'; break;
+        case '\n': next = 'n'; break;
+        case '\r': next = 'r'; break;
+        case '\t': next = 't'; break;
+        case '\v': next = 'v'; break;
+        case '\\': next = '\\'; break;
+        case '\'': next = '\''; break;
+        case '\"': next = '\"'; if(Q.S==escape::CSV) quote = '"'; break;
+        default:
+            if(!isprint(C)) {
+                // print three charator escape
+                strm<<"\\x"<<hexdigit(C>>4)<<hexdigit(C);
+            } else {
+                // literal
+                strm.put(C);
+            }
+            continue;
+        }
+        // print two charactor escape
+        strm.put(quote);
+        strm.put(next);
+    }
+
+    return strm;
+}
+
 }} //epics::pvData

src/misc/pv/typeCast.h

@@ -208,6 +208,35 @@ static FORCE_INLINE
 typename detail::print_convolute<T>::return_t
 print_cast(const T& v) { return detail::print_convolute<T>::op(v); }
 
+class escape;
+
+epicsShareFunc
+std::ostream& operator<<(std::ostream& strm, const escape& Q);
+
+//! Helper to print a string with escaping
+//! @code strm<<'"'<<escape(astring)<<'"' @endcode
+struct epicsShareClass escape
+{
+    enum style_t {
+        C,   // default
+        CSV, // a la RFC4180
+    };
+private:
+    const std::string& orig;
+    style_t S;
+public:
+    escape(const std::string& orig) :orig(orig), S(C) {}
+    ~escape();
+    //! Change escaping style
+    inline escape& style(style_t s) { S = s; return *this; }
+    //! print to string and return.  (alloc and copy)
+    std::string str() const;
+
+    friend
+    epicsShareFunc
+    std::ostream& operator<<(std::ostream& strm, const escape& Q);
+};
+
 }} // end namespace
 
 #endif // PVTYPECAST_H