diff --git a/src/libstore/build.cc b/src/libstore/build.cc
index d8f8826e1..e60ea2106 100644
--- a/src/libstore/build.cc
+++ b/src/libstore/build.cc
@@ -1379,7 +1379,7 @@ HookReply DerivationGoal::tryBuildHook()
             break;
         }
         s += "\n";
-        writeToStderr((unsigned char *) s.c_str(), s.size());
+        writeToStderr((unsigned char *) s.data(), s.size());
     }
 
     debug(format("hook reply is `%1%'") % reply);
@@ -2036,12 +2036,12 @@ void DerivationGoal::handleChildOutput(int fd, const string & data)
         (!hook && fd == builderOut.readSide))
     {
         if (verbosity >= buildVerbosity)
-            writeToStderr((unsigned char *) data.c_str(), data.size());
-        writeFull(fdLogFile, (unsigned char *) data.c_str(), data.size());
+            writeToStderr((unsigned char *) data.data(), data.size());
+        writeFull(fdLogFile, (unsigned char *) data.data(), data.size());
     }
 
     if (hook && fd == hook->fromHook.readSide)
-        writeToStderr((unsigned char *) data.c_str(), data.size());
+        writeToStderr((unsigned char *) data.data(), data.size());
 }
 
 
@@ -2409,7 +2409,7 @@ void SubstitutionGoal::handleChildOutput(int fd, const string & data)
 {
     assert(fd == logPipe.readSide);
     if (verbosity >= buildVerbosity)
-        writeToStderr((unsigned char *) data.c_str(), data.size());
+        writeToStderr((unsigned char *) data.data(), data.size());
     /* Don't write substitution output to a log file for now.  We
        probably should, though. */
 }
diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 14c8ba0bf..c2e999a6e 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -196,7 +196,7 @@ void LocalStore::addTempRoot(const Path & path)
     lockFile(fdTempRoots, ltWrite, true);
 
     string s = path + '\0';
-    writeFull(fdTempRoots, (const unsigned char *) s.c_str(), s.size());
+    writeFull(fdTempRoots, (const unsigned char *) s.data(), s.size());
 
     /* Downgrade to a read lock. */
     debug(format("downgrading to read lock on `%1%'") % fnTempRoots);
diff --git a/src/libstore/references.cc b/src/libstore/references.cc
index c1f9e3ba7..282b84893 100644
--- a/src/libstore/references.cc
+++ b/src/libstore/references.cc
@@ -69,7 +69,7 @@ void RefScanSink::operator () (const unsigned char * data, size_t len)
        fragment, so search in the concatenation of the tail of the
        previous fragment and the start of the current fragment. */
     string s = tail + string((const char *) data, len > refLength ? refLength : len);
-    search((const unsigned char *) s.c_str(), s.size(), hashes, seen);
+    search((const unsigned char *) s.data(), s.size(), hashes, seen);
 
     search(data, len, hashes, seen);
 
diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 6e9921ede..c77a12870 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -509,7 +509,7 @@ void RemoteStore::processStderr(Sink * sink, Source * source)
         if (msg == STDERR_WRITE) {
             string s = readString(from);
             if (!sink) throw Error("no sink");
-            (*sink)((const unsigned char *) s.c_str(), s.size());
+            (*sink)((const unsigned char *) s.data(), s.size());
         }
         else if (msg == STDERR_READ) {
             if (!source) throw Error("no source");
@@ -521,7 +521,7 @@ void RemoteStore::processStderr(Sink * sink, Source * source)
         }
         else {
             string s = readString(from);
-            writeToStderr((const unsigned char *) s.c_str(), s.size());
+            writeToStderr((const unsigned char *) s.data(), s.size());
         }
     }
     if (msg == STDERR_ERROR) {
diff --git a/src/libutil/hash.cc b/src/libutil/hash.cc
index bbfe7847f..697a6b475 100644
--- a/src/libutil/hash.cc
+++ b/src/libutil/hash.cc
@@ -136,7 +136,7 @@ string printHash32(const Hash & hash)
     Hash hash2(hash);
     unsigned int len = hashLength32(hash);
 
-    const char * chars = base32Chars.c_str();
+    const char * chars = base32Chars.data();
     
     string s(len, '0');
 
@@ -186,7 +186,7 @@ Hash parseHash32(HashType ht, const string & s)
 {
     Hash hash(ht);
 
-    const char * chars = base32Chars.c_str();
+    const char * chars = base32Chars.data();
 
     for (unsigned int i = 0; i < s.length(); ++i) {
         char c = s[i];
@@ -271,7 +271,7 @@ Hash hashString(HashType ht, const string & s)
     Ctx ctx;
     Hash hash(ht);
     start(ht, ctx);
-    update(ht, ctx, (const unsigned char *) s.c_str(), s.length());
+    update(ht, ctx, (const unsigned char *) s.data(), s.length());
     finish(ht, ctx, hash.hash);
     return hash;
 }
diff --git a/src/libutil/serialise.cc b/src/libutil/serialise.cc
index c4563ffd1..9270806a7 100644
--- a/src/libutil/serialise.cc
+++ b/src/libutil/serialise.cc
@@ -159,7 +159,7 @@ void writeString(const unsigned char * buf, size_t len, Sink & sink)
 
 void writeString(const string & s, Sink & sink)
 {
-    writeString((const unsigned char *) s.c_str(), s.size(), sink);
+    writeString((const unsigned char *) s.data(), s.size(), sink);
 }
 
 
diff --git a/src/libutil/util.cc b/src/libutil/util.cc
index 0352754f5..42e5519b4 100644
--- a/src/libutil/util.cc
+++ b/src/libutil/util.cc
@@ -236,7 +236,7 @@ void writeFile(const Path & path, const string & s)
     AutoCloseFD fd = open(path.c_str(), O_WRONLY | O_TRUNC | O_CREAT, 0666);
     if (fd == -1)
         throw SysError(format("opening file `%1%'") % path);
-    writeFull(fd, (unsigned char *) s.c_str(), s.size());
+    writeFull(fd, (unsigned char *) s.data(), s.size());
 }
 
 
@@ -263,7 +263,7 @@ string readLine(int fd)
 void writeLine(int fd, string s)
 {
     s += '\n';
-    writeFull(fd, (const unsigned char *) s.c_str(), s.size());
+    writeFull(fd, (const unsigned char *) s.data(), s.size());
 }
 
 
@@ -485,7 +485,7 @@ void printMsg_(Verbosity level, const format & f)
         prefix = "\033[" + escVerbosity(level) + "s";
     string s = (format("%1%%2%\n") % prefix % f.str()).str();
     try {
-        writeToStderr((const unsigned char *) s.c_str(), s.size());
+        writeToStderr((const unsigned char *) s.data(), s.size());
     } catch (SysError & e) {
         /* Ignore failing writes to stderr if we're in an exception
            handler, otherwise throw an exception.  We need to ignore
diff --git a/src/nix-store/nix-store.cc b/src/nix-store/nix-store.cc
index 2e1d3f044..404da2c51 100644
--- a/src/nix-store/nix-store.cc
+++ b/src/nix-store/nix-store.cc
@@ -432,7 +432,7 @@ static void opReadLog(Strings opFlags, Strings opArgs)
 
         /* !!! Make this run in O(1) memory. */
         string log = readFile(logPath);
-        writeFull(STDOUT_FILENO, (const unsigned char *) log.c_str(), log.size());
+        writeFull(STDOUT_FILENO, (const unsigned char *) log.data(), log.size());
     }
 }
 
diff --git a/src/nix-worker/nix-worker.cc b/src/nix-worker/nix-worker.cc
index f28905a24..eaa686667 100644
--- a/src/nix-worker/nix-worker.cc
+++ b/src/nix-worker/nix-worker.cc
@@ -135,7 +135,7 @@ static void sigPollHandler(int sigNo)
     catch (Error & e) {
         /* Shouldn't happen. */
         string s = "impossible: " + e.msg() + '\n';
-        write(STDERR_FILENO, s.c_str(), s.size());
+        write(STDERR_FILENO, s.data(), s.size());
         throw;
     }
 }