feat(ex04): it works

ex04/main.cpp

@@ -0,0 +1,56 @@
+#include <cstring>
+#include <fstream>
+#include <iostream>
+#include <string>
+
+int main(int argc, char *argv[]) {
+  if (argc != 4) {
+    std::cerr << "Usage: " << argv[0] << " <filename> <s1> <s2>" << std::endl;
+    return 2;
+  }
+
+  std::string in_filename = argv[1];
+  std::string out_filename = in_filename + ".replace";
+  std::string s1 = argv[2];
+  std::string s2 = argv[3];
+
+  std::ifstream infile(in_filename.c_str(), std::ios::in);
+
+  if (!infile.is_open()) {
+    std::cerr << "Failed to open file " << in_filename << ": "
+              << strerror(errno) << std::endl;
+    return 1;
+  }
+
+  std::ofstream outfile(out_filename.c_str());
+
+  if (!outfile.is_open()) {
+    std::cerr << "Failed to open file " << out_filename << ": "
+              << strerror(errno) << std::endl;
+    return 1;
+  }
+
+  std::string line;
+  while (!infile.eof() && !infile.fail()) {
+    if (infile.fail()) {
+      std::cerr << "Failed to read from file " << in_filename << ": "
+                << strerror(errno) << std::endl;
+      return 1;
+    }
+    std::getline(infile, line);
+    size_t pos = 0;
+    while (pos < line.length()) {
+      size_t offset = line.find(s1, pos);
+      outfile << line.substr(pos, offset - pos);
+      if (offset == std::string::npos) {
+        break;
+      }
+      outfile << s2;
+      pos = offset + s1.length();
+    }
+    if (!infile.eof() && !infile.fail())
+      outfile << std::endl;
+  }
+
+  return 0;
+}