Just use std exception.

src/cli_main.cc

@@ -441,11 +441,6 @@ class CLI {
 
     rabit::Init(argc, argv);
     std::string config_path = argv[1];
-    if (!common::CanReadFile(config_path)) {
-      std::cerr << "Failed to open config file: \"" << argv[1] << "\"\n"
-                << CliHelp();
-      exit(1);
-    }
 
     common::ConfigParser cp(config_path);
     auto cfg = cp.Parse();

src/common/config.h

@@ -41,9 +41,15 @@ class ConfigParser {
   std::string LoadConfigFile(const std::string& path) {
     std::ifstream fin(path, std::ios_base::in | std::ios_base::binary);
     CHECK(fin) << "Failed to open: " << path;
-    std::string content{std::istreambuf_iterator<char>(fin),
-                        std::istreambuf_iterator<char>()};
-    return content;
+    try {
+      std::string content{std::istreambuf_iterator<char>(fin),
+                          std::istreambuf_iterator<char>()};
+      return content;
+    } catch (std::ios_base::failure const &e) {
+      LOG(FATAL) << "Failed to read: \"" << path << "\"\n"
+                 << e.what();
+    }
+    return "";
   }
 
   /*!

src/common/io.cc

@@ -1,48 +1,19 @@
 /*!
- * Copyright (c) by XGBoost Contributors 2019-2020
+ * Copyright (c) by XGBoost Contributors 2019
  */
-#define XGBOOST_IS_UNIX()                       \
-  defined(__unix__) || defined(unix) || defined(__unix) || defined(__APPLE__)
-
-#if XGBOOST_IS_UNIX()
+#if defined(__unix__)
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <unistd.h>
-#include <sys/stat.h>
-#endif  // XGBOOST_IS_UNIX()
-
+#endif  // defined(__unix__)
 #include <algorithm>
 #include <cstdio>
-#include <cstdlib>
 #include <string>
 #include <utility>
 
 #include "xgboost/logging.h"
 #include "io.h"
 
-#ifndef S_ISDIR
-
-#ifdef _MSC_VER
-#include  <io.h>
-// from: https://www.linuxquestions.org/questions/programming-9/porting-to-win32-429334/
-#define XGBOOST_S_ISDIR(mode)  (((mode) & _S_IFMT) == _S_IFDIR)
-#endif  // _MSC_VER
-
-#else
-
-#define XGBOOST_S_ISDIR(mode)  S_ISDIR((mode))
-#endif  // S_ISDIR
-
-namespace {
-int Access(char const* path, int type) {
-#if defined(_MSC_VER)
-  return _access(path, type);
-#else
-  return access(path, type);
-#endif  // defined(_MSC_VER)
-}
-}  // anonymous namespace
-
 namespace xgboost {
 namespace common {
 
@@ -137,9 +108,7 @@ std::string LoadSequentialFile(std::string fname) {
                  };
 
   std::string buffer;
-  CHECK(CanReadFile(fname.c_str()))
-      << "Failed to read file: " << fname;
-#if XGBOOST_IS_UNIX()
+#if defined(__unix__)
   struct stat fs;
   if (stat(fname.c_str(), &fs) != 0) {
     OpenErr();
@@ -168,18 +137,10 @@ std::string LoadSequentialFile(std::string fname) {
   buffer.resize(fsize + 1);
   fread(&buffer[0], 1, fsize, f);
   fclose(f);
-#endif  // XGBOOST_IS_UNIX()
+#endif  // defined(__unix__)
   buffer.back() = '\0';
   return buffer;
 }
 
-bool CanReadFile(std::string const& path) {
-  struct stat path_stat;
-  stat(path.c_str(), &path_stat);
-  return Access(path.c_str(), 0) == 0 && !XGBOOST_S_ISDIR(path_stat.st_mode);
-}
 }  // namespace common
 }  // namespace xgboost
-
-#undef XGBOOST_S_ISDIR
-#undef XGBOOST_IS_UNIX

src/common/io.h

@@ -87,7 +87,6 @@ inline std::string FileExtension(std::string const& fname) {
   }
 }
 
-bool CanReadFile(std::string const& path);
 }  // namespace common
 }  // namespace xgboost
 #endif  // XGBOOST_COMMON_IO_H_

tests/cpp/common/test_io.cc

@@ -39,13 +39,5 @@ TEST(IO, FixedSizeStream) {
     ASSERT_EQ(huge_buffer, out_buffer);
   }
 }
-
-TEST(IO, CanReadFile) {
-  // Non-exist file.
-  ASSERT_FALSE(CanReadFile("foo"));
-  // Can't read directory
-  ASSERT_FALSE(CanReadFile("./"));
-  ASSERT_TRUE(CanReadFile(__FILE__));
-}
 }  // namespace common
 }  // namespace xgboost