diff --git a/src/AbstractDiskWriter.cc b/src/AbstractDiskWriter.cc
index 52efc012..0568bfae 100644
--- a/src/AbstractDiskWriter.cc
+++ b/src/AbstractDiskWriter.cc
@@ -258,7 +258,7 @@ ssize_t AbstractDiskWriter::writeDataInternal(const unsigned char* data,
                                               size_t len, int64_t offset)
 {
   if (mapaddr_) {
-    memcpy(mapaddr_ + offset, data, len);
+    std::copy_n(data, len, mapaddr_ + offset);
     return len;
   }
   else {
@@ -298,7 +298,7 @@ ssize_t AbstractDiskWriter::readDataInternal(unsigned char* data, size_t len,
       return 0;
     }
     auto readlen = std::min(maplen_ - offset, static_cast<int64_t>(len));
-    memcpy(data, mapaddr_ + offset, readlen);
+    std::copy_n(mapaddr_ + offset, readlen, data);
     return readlen;
   }
   else {
diff --git a/src/BitfieldMan.cc b/src/BitfieldMan.cc
index 43d3ba25..8d1d189b 100644
--- a/src/BitfieldMan.cc
+++ b/src/BitfieldMan.cc
@@ -64,8 +64,8 @@ BitfieldMan::BitfieldMan(int32_t blockLength, int64_t totalLength)
     bitfieldLength_ = blocks_ / 8 + (blocks_ % 8 ? 1 : 0);
     bitfield_ = new unsigned char[bitfieldLength_];
     useBitfield_ = new unsigned char[bitfieldLength_];
-    memset(bitfield_, 0, bitfieldLength_);
-    memset(useBitfield_, 0, bitfieldLength_);
+    std::fill_n(bitfield_, bitfieldLength_, 0);
+    std::fill_n(useBitfield_, bitfieldLength_, 0);
     updateCache();
   }
 }
@@ -85,11 +85,11 @@ BitfieldMan::BitfieldMan(const BitfieldMan& bitfieldMan)
       blockLength_(bitfieldMan.blockLength_),
       filterEnabled_(bitfieldMan.filterEnabled_)
 {
-  memcpy(bitfield_, bitfieldMan.bitfield_, bitfieldLength_);
-  memcpy(useBitfield_, bitfieldMan.useBitfield_, bitfieldLength_);
+  std::copy_n(bitfieldMan.bitfield_, bitfieldLength_, bitfield_);
+  std::copy_n(bitfieldMan.useBitfield_, bitfieldLength_, useBitfield_);
   if (filterEnabled_) {
     filterBitfield_ = new unsigned char[bitfieldLength_];
-    memcpy(filterBitfield_, bitfieldMan.filterBitfield_, bitfieldLength_);
+    std::copy_n(bitfieldMan.filterBitfield_, bitfieldLength_, filterBitfield_);
   }
   updateCache();
 }
@@ -105,16 +105,17 @@ BitfieldMan& BitfieldMan::operator=(const BitfieldMan& bitfieldMan)
 
     delete[] bitfield_;
     bitfield_ = new unsigned char[bitfieldLength_];
-    memcpy(bitfield_, bitfieldMan.bitfield_, bitfieldLength_);
+    std::copy_n(bitfieldMan.bitfield_, bitfieldLength_, bitfield_);
 
     delete[] useBitfield_;
     useBitfield_ = new unsigned char[bitfieldLength_];
-    memcpy(useBitfield_, bitfieldMan.useBitfield_, bitfieldLength_);
+    std::copy_n(bitfieldMan.useBitfield_, bitfieldLength_, useBitfield_);
 
     delete[] filterBitfield_;
     if (filterEnabled_) {
       filterBitfield_ = new unsigned char[bitfieldLength_];
-      memcpy(filterBitfield_, bitfieldMan.filterBitfield_, bitfieldLength_);
+      std::copy_n(bitfieldMan.filterBitfield_, bitfieldLength_,
+                  filterBitfield_);
     }
     else {
       filterBitfield_ = nullptr;
@@ -665,14 +666,14 @@ void BitfieldMan::setBitfield(const unsigned char* bitfield,
   if (bitfieldLength_ == 0 || bitfieldLength_ != bitfieldLength) {
     return;
   }
-  memcpy(bitfield_, bitfield, bitfieldLength_);
-  memset(useBitfield_, 0, bitfieldLength_);
+  std::copy_n(bitfield, bitfieldLength_, bitfield_);
+  std::fill_n(useBitfield_, bitfieldLength_, 0);
   updateCache();
 }
 
 void BitfieldMan::clearAllBit()
 {
-  memset(bitfield_, 0, bitfieldLength_);
+  std::fill_n(bitfield_, bitfieldLength_, 0);
   updateCache();
 }
 
@@ -686,7 +687,7 @@ void BitfieldMan::setAllBit()
 
 void BitfieldMan::clearAllUseBit()
 {
-  memset(useBitfield_, 0, bitfieldLength_);
+  std::fill_n(useBitfield_, bitfieldLength_, 0);
   updateCache();
 }
 
@@ -706,7 +707,7 @@ void BitfieldMan::ensureFilterBitfield()
 {
   if (!filterBitfield_) {
     filterBitfield_ = new unsigned char[bitfieldLength_];
-    memset(filterBitfield_, 0, bitfieldLength_);
+    std::fill_n(filterBitfield_, bitfieldLength_, 0);
   }
 }
 
diff --git a/src/PeerConnection.cc b/src/PeerConnection.cc
index 51f08a6f..56461fb2 100644
--- a/src/PeerConnection.cc
+++ b/src/PeerConnection.cc
@@ -142,7 +142,8 @@ bool PeerConnection::receiveMessage(unsigned char* data, size_t& dataLength)
     resbufOffset_ = i;
     if (done) {
       if (data) {
-        memcpy(data, resbuf_.get() + msgOffset_ + 4, currentPayloadLength_);
+        std::copy_n(resbuf_.get() + msgOffset_ + 4, currentPayloadLength_,
+                    data);
       }
       dataLength = currentPayloadLength_;
       return true;
@@ -220,7 +221,7 @@ bool PeerConnection::receiveHandshake(unsigned char* data, size_t& dataLength,
     }
   }
   size_t writeLength = std::min(resbufLength_, dataLength);
-  memcpy(data, resbuf_.get(), writeLength);
+  std::copy_n(resbuf_.get(), writeLength, data);
   dataLength = writeLength;
   if (retval && !peek) {
     resbufLength_ = 0;
@@ -249,7 +250,7 @@ void PeerConnection::enableEncryption(std::unique_ptr<ARC4Encryptor> encryptor,
 void PeerConnection::presetBuffer(const unsigned char* data, size_t length)
 {
   size_t nwrite = std::min(bufferCapacity_, length);
-  memcpy(resbuf_.get(), data, nwrite);
+  std::copy_n(data, nwrite, resbuf_.get());
   resbufLength_ = length;
 }
 
@@ -280,7 +281,7 @@ void PeerConnection::reserveBuffer(size_t minSize)
   if (bufferCapacity_ < minSize) {
     bufferCapacity_ = minSize;
     auto buf = make_unique<unsigned char[]>(bufferCapacity_);
-    memcpy(buf.get(), resbuf_.get(), resbufLength_);
+    std::copy_n(resbuf_.get(), resbufLength_, buf.get());
     resbuf_ = std::move(buf);
   }
 }