middle version

src/utils/io.h

@@ -92,11 +92,49 @@ class IStream {
 class ISeekStream: public IStream {
  public:
   /*! \brief seek to certain position of the file */
-  virtual void Seek(long pos) = 0;
+  virtual void Seek(size_t pos) = 0;
   /*! \brief tell the position of the stream */
-  virtual long Tell(void) = 0;
+  virtual size_t Tell(void) = 0;
 };
 
+/*! \brief a in memory buffer that can be read and write as stream interface */
+struct MemoryBufferStream : public ISeekStream {
+ public:
+  MemoryBufferStream(std::string *p_buffer) 
+      : p_buffer_(p_buffer) {
+    curr_ptr_ = 0;
+  }
+  virtual ~MemoryBufferStream(void) {}
+  virtual size_t Read(void *ptr, size_t size) {
+    utils::Assert(curr_ptr_ <= p_buffer_->length(),
+                  "read can not have position excceed buffer length");
+    size_t nread = std::min(p_buffer_->length() - curr_ptr_, size);
+    if (nread != 0) memcpy(ptr, &(*p_buffer_)[0] + curr_ptr_, nread);
+    curr_ptr_ += nread;
+    return nread;
+  }
+  virtual void Write(const void *ptr, size_t size) {
+    if (size == 0) return;
+    if (curr_ptr_ + size > p_buffer_->length()) {
+      p_buffer_->resize(curr_ptr_+size);
+    }
+    memcpy(&(*p_buffer_)[0] + curr_ptr_, ptr, size); 
+    curr_ptr_ += size;
+  }
+  virtual void Seek(size_t pos) {
+    curr_ptr_ = static_cast<size_t>(pos);
+  }
+  virtual size_t Tell(void) {
+    return curr_ptr_;
+  }
+
+ private:
+  /*! \brief in memory buffer */
+  std::string *p_buffer_;
+  /*! \brief current pointer */
+  size_t curr_ptr_;
+}; // class MemoryBufferStream
+
 /*! \brief implementation of file i/o stream */
 class FileStream : public ISeekStream {
  public:
@@ -110,10 +148,10 @@ class FileStream : public ISeekStream {
   virtual void Write(const void *ptr, size_t size) {
     std::fwrite(ptr, size, 1, fp);
   }
-  virtual void Seek(long pos) {
+  virtual void Seek(size_t pos) {
     std::fseek(fp, pos, SEEK_SET);
   }
-  virtual long Tell(void) {
+  virtual size_t Tell(void) {
     return std::ftell(fp);
   }
   inline void Close(void) {