diff --git a/src/qt/signverifymessagedialog.cpp b/src/qt/signverifymessagedialog.cpp
--- a/src/qt/signverifymessagedialog.cpp
+++ b/src/qt/signverifymessagedialog.cpp
@@ -161,7 +161,7 @@
                                 QString("</nobr>"));
 
     ui->signatureOut_SM->setText(
-        QString::fromStdString(EncodeBase64(&vchSig[0], vchSig.size())));
+        QString::fromStdString(EncodeBase64(vchSig.data(), vchSig.size())));
 }
 
 void SignVerifyMessageDialog::on_copySignatureButton_SM_clicked() {
diff --git a/src/qt/test/paymentservertests.cpp b/src/qt/test/paymentservertests.cpp
--- a/src/qt/test/paymentservertests.cpp
+++ b/src/qt/test/paymentservertests.cpp
@@ -7,12 +7,12 @@
 #include <amount.h>
 #include <interfaces/node.h>
 #include <qt/optionsmodel.h>
+#include <qt/test/paymentrequestdata.h>
 #include <random.h>
 #include <script/script.h>
 #include <script/standard.h>
 #include <util.h>
 #include <utilstrencodings.h>
-#include <qt/test/paymentrequestdata.h>
 
 #include <openssl/x509.h>
 #include <openssl/x509_vfy.h>
@@ -23,7 +23,7 @@
 X509 *parse_b64der_cert(const char *cert_data) {
     std::vector<uint8_t> data = DecodeBase64(cert_data);
     assert(data.size() > 0);
-    const uint8_t *dptr = &data[0];
+    const uint8_t *dptr = data.data();
     X509 *cert = d2i_X509(nullptr, &dptr, data.size());
     assert(cert);
     return cert;
@@ -42,7 +42,7 @@
     // Write data to a temp file:
     QTemporaryFile f;
     f.open();
-    f.write((const char *)&data[0], data.size());
+    f.write((const char *)data.data(), data.size());
     f.close();
 
     // Create a QObject, install event filter from PaymentServer and send a file
@@ -141,7 +141,7 @@
     // Contains a testnet paytoaddress, so payment request network doesn't match
     // client network:
     data = DecodeBase64(paymentrequest1_cert2_BASE64);
-    byteArray = QByteArray((const char *)&data[0], data.size());
+    byteArray = QByteArray((const char *)data.data(), data.size());
     r.paymentRequest.parse(byteArray);
     // Ensure the request is initialized, because network "main" is default,
     // even for uninitialized payment requests and that will fail our test here.
@@ -151,7 +151,7 @@
 
     // Expired payment request (expires is set to 1 = 1970-01-01 00:00:01):
     data = DecodeBase64(paymentrequest2_cert2_BASE64);
-    byteArray = QByteArray((const char *)&data[0], data.size());
+    byteArray = QByteArray((const char *)data.data(), data.size());
     r.paymentRequest.parse(byteArray);
     // Ensure the request is initialized
     QVERIFY(r.paymentRequest.IsInitialized());
@@ -164,7 +164,7 @@
     // (int32_t)
     // -1 is 1969-12-31 23:59:59 (for a 32 bit time values)
     data = DecodeBase64(paymentrequest3_cert2_BASE64);
-    byteArray = QByteArray((const char *)&data[0], data.size());
+    byteArray = QByteArray((const char *)data.data(), data.size());
     r.paymentRequest.parse(byteArray);
     // Ensure the request is initialized
     QVERIFY(r.paymentRequest.IsInitialized());
@@ -179,7 +179,7 @@
     // (int32_t)
     // 0 is 1970-01-01 00:00:00 (for a 32 bit time values)
     data = DecodeBase64(paymentrequest4_cert2_BASE64);
-    byteArray = QByteArray((const char *)&data[0], data.size());
+    byteArray = QByteArray((const char *)data.data(), data.size());
     r.paymentRequest.parse(byteArray);
     // Ensure the request is initialized
     QVERIFY(r.paymentRequest.IsInitialized());
@@ -200,7 +200,7 @@
 
     // Payment request with amount overflow (amount is set to 21000001 BCH):
     data = DecodeBase64(paymentrequest5_cert2_BASE64);
-    byteArray = QByteArray((const char *)&data[0], data.size());
+    byteArray = QByteArray((const char *)data.data(), data.size());
     r.paymentRequest.parse(byteArray);
     // Ensure the request is initialized
     QVERIFY(r.paymentRequest.IsInitialized());
diff --git a/src/rpc/misc.cpp b/src/rpc/misc.cpp
--- a/src/rpc/misc.cpp
+++ b/src/rpc/misc.cpp
@@ -308,7 +308,7 @@
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Sign failed");
     }
 
-    return EncodeBase64(&vchSig[0], vchSig.size());
+    return EncodeBase64(vchSig.data(), vchSig.size());
 }
 
 static UniValue setmocktime(const Config &config,
diff --git a/src/test/bip32_tests.cpp b/src/test/bip32_tests.cpp
--- a/src/test/bip32_tests.cpp
+++ b/src/test/bip32_tests.cpp
@@ -98,7 +98,7 @@
     std::vector<uint8_t> seed = ParseHex(test.strHexMaster);
     CExtKey key;
     CExtPubKey pubkey;
-    key.SetMaster(&seed[0], seed.size());
+    key.SetMaster(seed.data(), seed.size());
     pubkey = key.Neuter();
     for (const TestDerivation &derive : test.vDerive) {
         uint8_t data[74];
diff --git a/src/test/bloom_tests.cpp b/src/test/bloom_tests.cpp
--- a/src/test/bloom_tests.cpp
+++ b/src/test/bloom_tests.cpp
@@ -238,9 +238,9 @@
     COutPoint prevOutPoint(txid, 0);
     {
         std::vector<uint8_t> data(32 + sizeof(uint32_t));
-        memcpy(&data[0], prevOutPoint.GetTxId().begin(), 32);
+        memcpy(data.data(), prevOutPoint.GetTxId().begin(), 32);
         uint32_t n = prevOutPoint.GetN();
-        memcpy(&data[32], &n, sizeof(uint32_t));
+        memcpy(data.data() + 32, &n, sizeof(uint32_t));
         filter.insert(data);
     }
     BOOST_CHECK_MESSAGE(
diff --git a/src/test/crypto_tests.cpp b/src/test/crypto_tests.cpp
--- a/src/test/crypto_tests.cpp
+++ b/src/test/crypto_tests.cpp
@@ -74,14 +74,14 @@
 static void TestHMACSHA256(const std::string &hexkey, const std::string &hexin,
                            const std::string &hexout) {
     std::vector<uint8_t> key = ParseHex(hexkey);
-    TestVector(CHMAC_SHA256(&key[0], key.size()), ParseHex(hexin),
+    TestVector(CHMAC_SHA256(key.data(), key.size()), ParseHex(hexin),
                ParseHex(hexout));
 }
 
 static void TestHMACSHA512(const std::string &hexkey, const std::string &hexin,
                            const std::string &hexout) {
     std::vector<uint8_t> key = ParseHex(hexkey);
-    TestVector(CHMAC_SHA512(&key[0], key.size()), ParseHex(hexin),
+    TestVector(CHMAC_SHA512(key.data(), key.size()), ParseHex(hexin),
                ParseHex(hexout));
 }
 
@@ -95,13 +95,13 @@
     assert(key.size() == 16);
     assert(in.size() == 16);
     assert(correctout.size() == 16);
-    AES128Encrypt enc(&key[0]);
+    AES128Encrypt enc(key.data());
     buf.resize(correctout.size());
     buf2.resize(correctout.size());
-    enc.Encrypt(&buf[0], &in[0]);
+    enc.Encrypt(buf.data(), in.data());
     BOOST_CHECK_EQUAL(HexStr(buf), HexStr(correctout));
-    AES128Decrypt dec(&key[0]);
-    dec.Decrypt(&buf2[0], &buf[0]);
+    AES128Decrypt dec(key.data());
+    dec.Decrypt(buf2.data(), buf.data());
     BOOST_CHECK_EQUAL(HexStr(buf2), HexStr(in));
 }
 
@@ -115,12 +115,12 @@
     assert(key.size() == 32);
     assert(in.size() == 16);
     assert(correctout.size() == 16);
-    AES256Encrypt enc(&key[0]);
+    AES256Encrypt enc(key.data());
     buf.resize(correctout.size());
-    enc.Encrypt(&buf[0], &in[0]);
+    enc.Encrypt(buf.data(), in.data());
     BOOST_CHECK(buf == correctout);
-    AES256Decrypt dec(&key[0]);
-    dec.Decrypt(&buf[0], &buf[0]);
+    AES256Decrypt dec(key.data());
+    dec.Decrypt(buf.data(), buf.data());
     BOOST_CHECK(buf == in);
 }
 
@@ -134,8 +134,8 @@
     std::vector<uint8_t> realout(in.size() + AES_BLOCKSIZE);
 
     // Encrypt the plaintext and verify that it equals the cipher
-    AES128CBCEncrypt enc(&key[0], &iv[0], pad);
-    int size = enc.Encrypt(&in[0], in.size(), &realout[0]);
+    AES128CBCEncrypt enc(key.data(), iv.data(), pad);
+    int size = enc.Encrypt(in.data(), in.size(), realout.data());
     realout.resize(size);
     BOOST_CHECK(realout.size() == correctout.size());
     BOOST_CHECK_MESSAGE(realout == correctout,
@@ -143,8 +143,8 @@
 
     // Decrypt the cipher and verify that it equals the plaintext
     std::vector<uint8_t> decrypted(correctout.size());
-    AES128CBCDecrypt dec(&key[0], &iv[0], pad);
-    size = dec.Decrypt(&correctout[0], correctout.size(), &decrypted[0]);
+    AES128CBCDecrypt dec(key.data(), iv.data(), pad);
+    size = dec.Decrypt(correctout.data(), correctout.size(), decrypted.data());
     decrypted.resize(size);
     BOOST_CHECK(decrypted.size() == in.size());
     BOOST_CHECK_MESSAGE(decrypted == in,
@@ -155,11 +155,12 @@
     for (std::vector<uint8_t>::iterator i(in.begin()); i != in.end(); ++i) {
         std::vector<uint8_t> sub(i, in.end());
         std::vector<uint8_t> subout(sub.size() + AES_BLOCKSIZE);
-        int _size = enc.Encrypt(&sub[0], sub.size(), &subout[0]);
+        int _size = enc.Encrypt(sub.data(), sub.size(), subout.data());
         if (_size != 0) {
             subout.resize(_size);
             std::vector<uint8_t> subdecrypted(subout.size());
-            _size = dec.Decrypt(&subout[0], subout.size(), &subdecrypted[0]);
+            _size =
+                dec.Decrypt(subout.data(), subout.size(), subdecrypted.data());
             subdecrypted.resize(_size);
             BOOST_CHECK(decrypted.size() == in.size());
             BOOST_CHECK_MESSAGE(subdecrypted == sub, HexStr(subdecrypted) +
@@ -179,8 +180,8 @@
     std::vector<uint8_t> realout(in.size() + AES_BLOCKSIZE);
 
     // Encrypt the plaintext and verify that it equals the cipher
-    AES256CBCEncrypt enc(&key[0], &iv[0], pad);
-    int size = enc.Encrypt(&in[0], in.size(), &realout[0]);
+    AES256CBCEncrypt enc(key.data(), iv.data(), pad);
+    int size = enc.Encrypt(in.data(), in.size(), realout.data());
     realout.resize(size);
     BOOST_CHECK(realout.size() == correctout.size());
     BOOST_CHECK_MESSAGE(realout == correctout,
@@ -188,8 +189,8 @@
 
     // Decrypt the cipher and verify that it equals the plaintext
     std::vector<uint8_t> decrypted(correctout.size());
-    AES256CBCDecrypt dec(&key[0], &iv[0], pad);
-    size = dec.Decrypt(&correctout[0], correctout.size(), &decrypted[0]);
+    AES256CBCDecrypt dec(key.data(), iv.data(), pad);
+    size = dec.Decrypt(correctout.data(), correctout.size(), decrypted.data());
     decrypted.resize(size);
     BOOST_CHECK(decrypted.size() == in.size());
     BOOST_CHECK_MESSAGE(decrypted == in,
@@ -200,11 +201,12 @@
     for (std::vector<uint8_t>::iterator i(in.begin()); i != in.end(); ++i) {
         std::vector<uint8_t> sub(i, in.end());
         std::vector<uint8_t> subout(sub.size() + AES_BLOCKSIZE);
-        int _size = enc.Encrypt(&sub[0], sub.size(), &subout[0]);
+        int _size = enc.Encrypt(sub.data(), sub.size(), subout.data());
         if (_size != 0) {
             subout.resize(_size);
             std::vector<uint8_t> subdecrypted(subout.size());
-            _size = dec.Decrypt(&subout[0], subout.size(), &subdecrypted[0]);
+            _size =
+                dec.Decrypt(subout.data(), subout.size(), subdecrypted.data());
             subdecrypted.resize(_size);
             BOOST_CHECK(decrypted.size() == in.size());
             BOOST_CHECK_MESSAGE(subdecrypted == sub, HexStr(subdecrypted) +
diff --git a/src/test/getarg_tests.cpp b/src/test/getarg_tests.cpp
--- a/src/test/getarg_tests.cpp
+++ b/src/test/getarg_tests.cpp
@@ -29,7 +29,7 @@
         vecChar.push_back(s.c_str());
     }
 
-    gArgs.ParseParameters(vecChar.size(), &vecChar[0]);
+    gArgs.ParseParameters(vecChar.size(), vecChar.data());
 }
 
 BOOST_AUTO_TEST_CASE(boolarg) {
diff --git a/src/test/skiplist_tests.cpp b/src/test/skiplist_tests.cpp
--- a/src/test/skiplist_tests.cpp
+++ b/src/test/skiplist_tests.cpp
@@ -40,7 +40,7 @@
         BOOST_CHECK(vIndex[SKIPLIST_LENGTH - 1].GetAncestor(from) ==
                     &vIndex[from]);
         BOOST_CHECK(vIndex[from].GetAncestor(to) == &vIndex[to]);
-        BOOST_CHECK(vIndex[from].GetAncestor(0) == &vIndex[0]);
+        BOOST_CHECK(vIndex[from].GetAncestor(0) == vIndex.data());
     }
 }
 
@@ -71,7 +71,8 @@
         // Add 1<<128 to the hashes, so GetLow64() still returns the height.
         vHashSide[i] = ArithToUint256(i + 50000 + (arith_uint256(1) << 128));
         vBlocksSide[i].nHeight = i + 50000;
-        vBlocksSide[i].pprev = i ? &vBlocksSide[i - 1] : &vBlocksMain[49999];
+        vBlocksSide[i].pprev =
+            i ? &vBlocksSide[i - 1] : (vBlocksMain.data() + 49999);
         vBlocksSide[i].phashBlock = &vHashSide[i];
         vBlocksSide[i].BuildSkip();
         BOOST_CHECK_EQUAL(
diff --git a/src/test/test_bitcoin_fuzzy.cpp b/src/test/test_bitcoin_fuzzy.cpp
--- a/src/test/test_bitcoin_fuzzy.cpp
+++ b/src/test/test_bitcoin_fuzzy.cpp
@@ -65,7 +65,7 @@
     if (buffer.size() < sizeof(uint32_t)) return 0;
 
     uint32_t test_id = 0xffffffff;
-    memcpy(&test_id, &buffer[0], sizeof(uint32_t));
+    memcpy(&test_id, buffer.data(), sizeof(uint32_t));
     buffer.erase(buffer.begin(), buffer.begin() + sizeof(uint32_t));
 
     if (test_id >= TEST_ID_END) return 0;
diff --git a/src/uint256.cpp b/src/uint256.cpp
--- a/src/uint256.cpp
+++ b/src/uint256.cpp
@@ -13,7 +13,7 @@
 template <unsigned int BITS>
 base_blob<BITS>::base_blob(const std::vector<uint8_t> &vch) {
     assert(vch.size() == sizeof(data));
-    memcpy(data, &vch[0], sizeof(data));
+    memcpy(data, vch.data(), sizeof(data));
 }
 
 template <unsigned int BITS> std::string base_blob<BITS>::GetHex() const {
diff --git a/src/wallet/crypter.cpp b/src/wallet/crypter.cpp
--- a/src/wallet/crypter.cpp
+++ b/src/wallet/crypter.cpp
@@ -28,9 +28,7 @@
     CSHA512 di;
 
     di.Write((const uint8_t *)strKeyData.c_str(), strKeyData.size());
-    if (chSalt.size()) {
-        di.Write(&chSalt[0], chSalt.size());
-    }
+    di.Write(chSalt.data(), chSalt.size());
     di.Finalize(buf);
 
     for (int i = 0; i != count - 1; i++) {
@@ -92,8 +90,8 @@
     vchCiphertext.resize(vchPlaintext.size() + AES_BLOCKSIZE);
 
     AES256CBCEncrypt enc(vchKey.data(), vchIV.data(), true);
-    size_t nLen =
-        enc.Encrypt(&vchPlaintext[0], vchPlaintext.size(), &vchCiphertext[0]);
+    size_t nLen = enc.Encrypt(vchPlaintext.data(), vchPlaintext.size(),
+                              vchCiphertext.data());
     if (nLen < vchPlaintext.size()) {
         return false;
     }
@@ -114,8 +112,8 @@
     vchPlaintext.resize(nLen);
 
     AES256CBCDecrypt dec(vchKey.data(), vchIV.data(), true);
-    nLen =
-        dec.Decrypt(&vchCiphertext[0], vchCiphertext.size(), &vchPlaintext[0]);
+    nLen = dec.Decrypt(vchCiphertext.data(), vchCiphertext.size(),
+                       vchPlaintext.data());
     if (nLen == 0) {
         return false;
     }
@@ -129,7 +127,7 @@
                           std::vector<uint8_t> &vchCiphertext) {
     CCrypter cKeyCrypter;
     std::vector<uint8_t> chIV(WALLET_CRYPTO_IV_SIZE);
-    memcpy(&chIV[0], &nIV, WALLET_CRYPTO_IV_SIZE);
+    memcpy(chIV.data(), &nIV, WALLET_CRYPTO_IV_SIZE);
     if (!cKeyCrypter.SetKey(vMasterKey, chIV)) {
         return false;
     }
@@ -142,7 +140,7 @@
                           const uint256 &nIV, CKeyingMaterial &vchPlaintext) {
     CCrypter cKeyCrypter;
     std::vector<uint8_t> chIV(WALLET_CRYPTO_IV_SIZE);
-    memcpy(&chIV[0], &nIV, WALLET_CRYPTO_IV_SIZE);
+    memcpy(chIV.data(), &nIV, WALLET_CRYPTO_IV_SIZE);
     if (!cKeyCrypter.SetKey(vMasterKey, chIV)) {
         return false;
     }
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -736,7 +736,7 @@
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Sign failed");
     }
 
-    return EncodeBase64(&vchSig[0], vchSig.size());
+    return EncodeBase64(vchSig.data(), vchSig.size());
 }
 
 static UniValue getreceivedbyaddress(const Config &config,
diff --git a/src/wallet/test/wallet_crypto_tests.cpp b/src/wallet/test/wallet_crypto_tests.cpp
--- a/src/wallet/test/wallet_crypto_tests.cpp
+++ b/src/wallet/test/wallet_crypto_tests.cpp
@@ -107,7 +107,7 @@
 
     std::string hash(GetRandHash().ToString());
     std::vector<uint8_t> vchSalt(8);
-    GetRandBytes(&vchSalt[0], vchSalt.size());
+    GetRandBytes(vchSalt.data(), vchSalt.size());
     uint32_t rounds = InsecureRand32();
     if (rounds > 30000) rounds = 30000;
     TestCrypter::TestPassphrase(vchSalt, SecureString(hash.begin(), hash.end()),