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Thinking in C++, 2nd ed., Volume 2, Revision 3

©2000 by Bruce Eckel

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//: :require.h
// Test for error conditions in programs
// Local "using namespace std" for old compilers
#ifndef REQUIRE_H
#define REQUIRE_H
#include <cstdio>
#include <cstdlib>
#include <fstream>

inline void require(bool requirement, 
  const char* msg = "Requirement failed") {
  using namespace std;
  if (!requirement) {
    fputs(msg, stderr);
    fputs("\n", stderr);
    exit(1);
  }
}

inline void requireArgs(int argc, int args, 
  const char* msg = "Must use %d arguments") {
  using namespace std;
   if (argc != args + 1) {
     fprintf(stderr, msg, args);
     fputs("\n", stderr);
     exit(1);
   }
}

inline void requireMinArgs(int argc, int minArgs,
  const char* msg = 
    "Must use at least %d arguments") {
  using namespace std;
  if(argc < minArgs + 1) {
    fprintf(stderr, msg, minArgs);
    fputs("\n", stderr);
    exit(1);
  }
}
  
inline void assure(std::ifstream& in, 
  const char* filename = "") {
  using namespace std;
  if(!in) {
    fprintf(stderr,
      "Could not open file %s\n", filename);
    exit(1);
  }
}

inline void assure(std::ofstream& in, 
  const char* filename = "") {
  using namespace std;
  if(!in) {
    fprintf(stderr,
      "Could not open file %s\n", filename);
    exit(1);
  }
}

//: C0A:Stack4.h
// With inlines
#ifndef STACK4_H
#define STACK4_H
#include "../require.h"

class Stack {
  struct Link {
    void* data;
    Link* next;
    Link(void* dat, Link* nxt): 
      data(dat), next(nxt) {}
  }* head;
public:
  Stack(){ head = 0; }
  ~Stack(){ 
    require(head == 0, "Stack not empty");
  }
  void push(void* dat) {
    head = new Link(dat, head);
  }
  void* peek() { return head->data; }
  void* pop(){
    if(head == 0) return 0;
    void* result = head->data;
    Link* oldHead = head;
    head = head->next;
    delete oldHead;
    return result;
  }
};

//: C0A:Dummy.cpp
// To give the makefile at least one target 
// for this directory