I/O Stream 应试向整理

I/O stream integration

stdin stream

deal with separately in a cpp form

string temp;
while(cin>>temp){
    cout<<temp<<" ";
    if (getchar()=='\n')
    break;
}
cout<<endl;

deal with altogether

string s;
int i=1;
while(getline(cin,s)){
    cout<<i<<" "<<s<<"\n";
    i++;
}
return 0;

input from file

C-style method

void P4(){
    FILE *fp = fopen("P4.txt", "r");
    FILE *output = fopen("P4_encrypt.txt", "w+");
    char temp{};
    while (1){
        temp = fgetc(fp);
        if (feof(fp)) break;
        if (temp == '.') fprintf(output, "%c", '?');
        else if (temp == '?') fprintf(output, "%c", '.');
        else if (temp == ' ') fprintf(output, "%c", '&');
        else if ((temp <= 'z' && temp >= 'a') || (temp <= '9' && temp >= '0'))
            fprintf(output, "%c", temp - 1);
        else fprintf(output, "%c", temp);
    }
    fclose(fp);
    fclose(output);
}

include<fstream>(if not required to deal with elements separately)

int main() {
    ifstream in("class.cpp");
    ofstream out("withNumber.cpp");
    string s{};
    int i=1;
    while(getline(in,s)){
        out<<i<<"   "<<s<<"\n";
        i++;
    }
    return 0;
}

include<fstream>(but required to deal with elements separately with xs branket)

#include <iostream>
#include <fstream>
#include <sstream>
#include <vector>
using namespace std;
int main(){
    string line;
    ifstream in("p3.txt");
    while (getline(in, line)){
        vector<int> numbers;
        int i, sum = 0;
        istringstream get(line);
        while (get >> i) numbers.push_back(i);
        for (auto number : numbers) sum += number;
        cout << sum << endl;
    }
    return 0;
}

an inefficient way of C-style(if required to deal with elements separately with xs branket)

FILE *fp = fopen("P3.txt", "r");
char temp[256];
while (getline(fp,temp)){
    while (temp[0] == ' ')
        for (int i = 1; i < 256; i++)
            temp[i - 1] = temp[i];
    for (int i = 5; i > 0; i--)
        if (temp[i] == '\0' && temp[i - 1] == ' ')
            temp[i - 1] = '\0';
    for (int i = 1; i < 255; i++){
        if (temp[i] == ' ' && temp[i + 1] == ' '){
            for (int j = i + 1; j < 256; j++)
                temp[j] = temp[j + 1];
            i--;
        }
    }
    int result = 0;
    int intTemp = 0;
    while (sscanf(temp, "%i", &intTemp)){
        result += intTemp;
        while (temp[0] != ' ' && temp[0] != '\n' && temp[0] != '\0')
            for (int i = 1; i < 256; i++)
                temp[i - 1] = temp[i];
        char car{};
        sscanf(temp, "%c", &car);
        if (car == '\0' || car == '\n') break;
        for (int i = 1; i < 256; i++) temp[i - 1] = temp[i];
    }
    cout << result << endl;
}