feat(ex04): it works

ex04/.gitignore

@@ -0,0 +1,3 @@
+ex04
+*.txt
+*.replace

ex04/Makefile

@@ -0,0 +1,38 @@
+NAME = ex04
+ifeq ($(CPPFLAGS),)
+	CPPFLAGS = -Wall -Wextra -Werror -std=c++98 -g
+endif
+ifeq ($(CXX),)
+	CXX = c++
+endif
+# g++ is the default on 42 computers
+ifeq ($(CXX),g++)
+	CXX = c++
+endif
+srcs = \
+
+main_objs = main.o $(srcs:.cpp=.o)
+all_objs = $(main_objs)
+deps = $(all_objs:.o=.d)
+
+all: $(NAME)
+
+-include $(deps)
+
+$(NAME): $(main_objs)
+	$(CXX) $(CPPFLAGS) -o $@ $^
+
+%.o: %.cpp
+	$(CXX) -c $(CPPFLAGS) -o $*.o $*.cpp
+	$(CXX) -MM $(CPPFLAGS) -MT $*.o $*.cpp > $*.d
+
+clean:
+	find . -name '*.o' -print -delete
+	find . -name '*.d' -print -delete
+
+fclean: clean
+	rm -f $(NAME)
+
+re:
+	+make fclean
+	+make all

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;
+}