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Thinking in C++ Vol 2 - Practical Programming
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Detecting compiler errors

All the code in this book is designed to compile as shown without errors. Lines of code that should generate a compile-time error may be commented out with the special comment sequence //! . The following program will remove these special comments and append a numbered comment to the line. When you run your compiler, it should generate error messages, and you will see all the numbers appear when you compile all the files. This program also appends the modified line to a special file so that you can easily locate any lines that don t generate errors.

//: C04:Showerr.cpp {RunByHand}
// Un-comment error generators.
#include <cstddef>
#include <cstdlib>
#include <cstdio>
#include <fstream>
#include <iostream>
#include <sstream>
#include <string>
#include "../require.h"
using namespace std;
const string USAGE =
"usage: showerr filename chapnum\n"
"where filename is a C++ source file\n"
"and chapnum is the chapter name it's in.\n"
"Finds lines commented with //! and removes\n"
"the comment, appending //(#) where # is unique\n"
"across all files, so you can determine\n"
"if your compiler finds the error.\n"
"showerr /r\n"
"resets the unique counter.";
class Showerr {
const int CHAP;
const string MARKER, FNAME;
// File containing error number counter:
const string ERRNUM;
// File containing error lines:
const string ERRFILE;
stringstream edited; // Edited file
int counter;
Showerr(const string& f, const string& en,
const string& ef, int c)
: CHAP(c), MARKER("//!"), FNAME(f), ERRNUM(en),
ERRFILE(ef), counter(0) {}
void replaceErrors() {
ifstream infile(FNAME.c_str());
assure(infile, FNAME.c_str());
ifstream count(ERRNUM.c_str());
if(count) count >> counter;
int linecount = 1;
string buf;
ofstream errlines(ERRFILE.c_str(), ios::app);
assure(errlines, ERRFILE.c_str());
while(getline(infile, buf)) {
// Find marker at start of line:
size_t pos = buf.find(MARKER);
if(pos != string::npos) {
// Erase marker:
buf.erase(pos, MARKER.size() + 1);
// Append counter & error info:
ostringstream out;
out << buf << " // (" << ++counter << ") "
<< "Chapter " << CHAP
<< " File: " << FNAME
<< " Line " << linecount << endl;
edited << out.str();
errlines << out.str(); // Append error file
edited << buf << "\n"; // Just copy
void saveFiles() {
ofstream outfile(FNAME.c_str()); // Overwrites
assure(outfile, FNAME.c_str());
outfile << edited.rdbuf();
ofstream count(ERRNUM.c_str()); // Overwrites
assure(count, ERRNUM.c_str());
count << counter; // Save new counter
int main(int argc, char* argv[]) {
const string ERRCOUNT("../errnum.txt"),
requireMinArgs(argc, 1, USAGE.c_str());
if(argv[1][0] == '/' || argv[1][0] == '-') {
// Allow for other switches:
switch(argv[1][1]) {
case 'r': case 'R':
cout << "reset counter" << endl;
remove(ERRCOUNT.c_str()); // Delete files
cerr << USAGE << endl;
if(argc == 3) {
Showerr s(argv[1], ERRCOUNT, ERRFILE, atoi(argv[2]));
} ///:~

You can replace the marker with one of your choice.

Each file is read a line at a time, and each line is searched for the marker appearing at the head of the line; the line is modified and put into the error line list and into the string stream, edited. When the whole file is processed, it is closed (by reaching the end of a scope), it is reopened as an output file, and edited is poured into the file. Also notice the counter is saved in an external file. The next time this program is invoked, it continues to increment the counter.

Thinking in C++ Vol 2 - Practical Programming
Prev Home Next

   Reproduced courtesy of Bruce Eckel, MindView, Inc. Design by Interspire