Thoughts on C ++ Primer's 10.3.9 word Conversion

#include <iostream>#include <string>#include <map>#include <fstream>#include <sstream>using namespace std;ifstream& open_file(ifstream&,const string&);int main(int argc, char **argv){    map<string, string> trans_map;    string key, value;    if (argc!= 3)        throw runtime_error("wrong number of arguments");    ifstream map_file;    if (!open_file(map_file, argv[1]))        throw runtime_error("no transformation file");    while (map_file>>key>>value)        trans_map.insert(make_pair(key, value));    ifstream input;    if (!open_file(input, argv[2]))        throw runtime_error("no input file");    string line;     while (getline(input, line))    {        istringstream stream(line);         string word;        bool firstword = true;        while (stream >> word) {            map<string, string>::const_iterator map_it =trans_map.find(word);            if (map_it != trans_map.end())                word = map_it->second;            if (firstword)                firstword = false;            else                cout << " ";            cout << word;        }        cout << endl;     }    return 0;}

This code has several knowledge points to review:

1. main Function Parameters

Main (int argc, char ** argv );

ArgcIs an integer variable, which refers to the number of input parameters in the command line,ArgvIs a string array that containsArgc stringsEach string stores a command line parameter, which can also be written as char * argv []. For example, argv [0] stores the first command line parameter string, argv [1] stores the second command line parameter string, argv [argc-1] stores the last command line parameter string. In general, argv [0] stores the path and full name of the current program.

Argc and argv are names that can be changed, such as arc and arv.