refactor: Remove locale-dependent function calls

Changes suggested in
bitcoin/bitcoin#31741 (comment) to be able
to enable more linters in Bitcoin Core CI.

Author: vasild

example/calculator.cpp

@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <calculator.h>
+#include <charconv>
 #include <fstream>
 #include <init.capnp.h>
 #include <init.capnp.proxy.h> // NOLINT(misc-include-cleaner)
@@ -44,8 +45,12 @@ int main(int argc, char** argv)
         std::cout << "Usage: mpcalculator <fd>\n";
         return 1;
     }
+    int fd;
+    if (std::from_chars(argv[1], argv[1] + strlen(argv[1]), fd).ec != std::errc{}) {
+        std::cout << argv[1] << " is not a number or is larger than an int\n";
+        return 1;
+    }
     mp::EventLoop loop("mpcalculator", LogPrint);
-    const int fd = std::stoi(argv[1]);
     std::unique_ptr<Init> init = std::make_unique<InitImpl>();
     mp::ServeStream<InitInterface>(loop, fd, *init);
     loop.loop();

example/example.cpp

@@ -25,7 +25,7 @@ static auto Spawn(mp::EventLoop& loop, const std::string& process_argv0, const s
         fs::path path = process_argv0;
         path.remove_filename();
         path.append(new_exe_name);
-        return {path.string(), std::to_string(fd)};
+        return {path.string(), std::format("{:d}", fd)};
     });
     return std::make_tuple(mp::ConnectStream<InitInterface>(loop, fd), pid);
 }

example/printer.cpp

@@ -3,6 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include <fstream>
+#include <charconv>
 #include <init.capnp.h>
 #include <init.capnp.proxy.h> // NOLINT(misc-include-cleaner)
 #include <init.h>
@@ -37,8 +38,12 @@ int main(int argc, char** argv)
         std::cout << "Usage: mpprinter <fd>\n";
         return 1;
     }
+    int fd;
+    if (std::from_chars(argv[1], argv[1] + strlen(argv[1]), fd).ec != std::errc{}) {
+        std::cout << argv[1] << " is not a number or is larger than an int\n";
+        return 1;
+    }
     mp::EventLoop loop("mpprinter", LogPrint);
-    const int fd = std::stoi(argv[1]);
     std::unique_ptr<Init> init = std::make_unique<InitImpl>();
     mp::ServeStream<InitInterface>(loop, fd, *init);
     loop.loop();

src/mp/gen.cpp

@@ -13,6 +13,7 @@
 #include <errno.h>
 #include <fstream>
 #include <functional>
+#include <iostream>
 #include <kj/array.h>
 #include <kj/common.h>
 #include <kj/filesystem.h>
@@ -637,7 +638,7 @@ static void Generate(kj::StringPtr src_prefix,
 int main(int argc, char** argv)
 {
     if (argc < 3) {
-        fprintf(stderr, "Usage: " PROXY_BIN " SRC_PREFIX INCLUDE_PREFIX SRC_FILE [IMPORT_PATH...]\n");
+        std::cerr << "Usage: " << PROXY_BIN << " SRC_PREFIX INCLUDE_PREFIX SRC_FILE [IMPORT_PATH...]\n";
         exit(1);
     }
     std::vector<kj::StringPtr> import_paths;

src/mp/util.cpp

@@ -6,6 +6,7 @@
 #include <mp/util.h>
 
 #include <errno.h>
+#include <format>
 #include <kj/common.h>
 #include <kj/string-tree.h>
 #include <pthread.h>
@@ -85,9 +86,7 @@ std::string LogEscape(const kj::StringTree& string)
             if (c == '\\') {
                 result.append("\\\\");
             } else if (c < 0x20 || c > 0x7e) {
-                char escape[4];
-                snprintf(escape, 4, "\\%02x", c);
-                result.append(escape);
+                result.append(std::format("\\{:02x}", c));
             } else {
                 result.push_back(c);
             }

test/mp/test/test.cpp

@@ -11,6 +11,7 @@
 #include <cstdio>
 #include <future>
 #include <functional>
+#include <iostream>
 #include <memory>
 #include <kj/common.h>
 #include <kj/memory.h>
@@ -27,7 +28,9 @@ KJ_TEST("Call FooInterface methods")
     std::promise<std::unique_ptr<ProxyClient<messages::FooInterface>>> foo_promise;
     std::function<void()> disconnect_client;
     std::thread thread([&]() {
-        EventLoop loop("mptest", [](bool raise, const std::string& log) { printf("LOG%i: %s\n", raise, log.c_str()); });
+        EventLoop loop("mptest", [](bool raise, const std::string& log) {
+            std::cout << "LOG" << raise << ": " << log << "\n";
+        });
         auto pipe = loop.m_io_context.provider->newTwoWayPipe();
 
         auto connection_client = std::make_unique<Connection>(loop, kj::mv(pipe.ends[0]));