为什么我在用 C++ 编写此文件处理代码后得到空白输出？
Why am i getting blank output after writing this filehandling code in c++?
我制作了一个测试器 class，我从问题池文本文件中提取问题，然后将其中的随机问题放入 docx 文件中。我想知道为什么我的代码在 docx 文件中给出空白输出。
我的随机函数工作正常。我从三个问题文件中选择两个两个问题。
这是我的代码 - `
void test()
{
string line;
fstream question1("questiondesc.txt",ios::in | ios::out | ios::app);
fstream testgen("GeneratedTest.docx",ios::trunc | ios::in | ios::out);
testgen.open("GeneratedTest.docx");
if(!question1.is_open())
{
question1.open("questiondesc.txt");
}
int i,num;
for (i = 0; i < 2; i++) {
num = random(1,12);
for(int i =1;i<=num;i++)
{
getline(question1,line);
}
question1.clear();
question1.seekg(0, ios::beg);
testgen<<line<<endl;
}
question1.close();
ifstream question2("questionmcq.txt");
if(!question2.is_open())
{
question2.open("questionmcq.txt");
}
for (i = 0; i < 2; i++) {
num = random(1,26);
while(num%2==0)
{
num = random(1,26);
}
for(int i =1;i<=num;i++)
{
getline(question2,line);
}
testgen<<line<<endl;
getline(question2,line);
testgen<<line<<endl;
question2.clear();
question2.seekg(0, ios::beg);
}
question2.close();
ifstream question3("questionanalytical.txt");
if(!question3.is_open())
{
question3.open("questionanalytical.txt");
}
for (i = 0; i < 2; i++) {
num = random(1,12);
for(int i =1;i<=num;i++)
{
getline(question3,line);
}
question3.clear();
question3.seekg(0, ios::beg);
testgen<<line<<endl;
}
question3.close();
testgen.close();
}
您的代码中有错误。我将在下面的列表中将它们显示为评论。此外，我将展示（许多，也许不是最好的）解决方案来解决您的问题。
你应该把你的问题分解成更小的部分并设计更多的功能。那样的话，生活会更轻松。
另外。你应该写评论。如果你写评论，那么你会自己发现问题。
你的代码加上我的备注：
#include <iostream>
#include <fstream>
#include <string>
#include <random>
using namespace std; // NO NEVER USE
int random(int from, int to) {
std::random_device random_device;
std::mt19937 generator(random_device());
std::uniform_int_distribution<int> distribution(from, to);
return distribution(generator);
}
void test()
{
string line; // Line is not initialized an not needed here. Pollutes namespace
fstream question1("questiondesc.txt", ios::in | ios::out | ios::app); // Opening a file with these flags will fail. Use ifstream
fstream testgen("GeneratedTest.docx", ios::trunc | ios::in | ios::out);// Opening a file with these flags will fail. Use ofstream
testgen.open("GeneratedTest.docx"); // File was alread opened and failed. Reopening will not work. It failed alread
if (!question1.is_open()) // Use if "(!question1)" instead. There could be also other error bits
{ // Always check the status of any IO operation
question1.open("questiondesc.txt"); // Will never work. Failer already
}
int i, num; // Variable not initialized and not needed here. Name space pollution
for (i = 0; i < 2; i++) {
num = random(1, 12); // This function was not defined. I redefined it
for (int i = 1; i <= num; i++) // i=1 and i<= reaaly) not i=0 and i<num?
{
getline(question1, line); // Always check status of any IO function
}
question1.clear();
question1.seekg(0, ios::beg);
testgen << line << endl;
}
question1.close(); // The destructor of the fstream will close the file for you
ifstream question2("questionmcq.txt"); // Now you open the file as ifstream
if (!question2.is_open()) // Do check for all possible flags.: If (!question2)
{
question2.open("questionmcq.txt"); // Will not work, if it failed in the first time
}
for (i = 0; i < 2; i++) { // So 2 times
num = random(1, 26);
while (num % 2 == 0) // If numbers are equal
{
num = random(1, 26); // Get an odd number
}
for (int i = 1; i <= num; i++) // Usually from 0 to <num
{
getline(question2, line);
}
testgen << line << endl;
getline(question2, line);
testgen << line << endl;
question2.clear();
question2.seekg(0, ios::beg);
}
question2.close(); // No need to close. Destructor will do it for you
ifstream question3("questionanalytical.txt"); // Now you open the file as ifstream
if (!question3.is_open()) // Wrong check. Check for all flags
{
question3.open("questionanalytical.txt"); // Will not help in case of failure
}
// Now this is the 3rd time with the same code. So, put it into a function
for (i = 0; i < 2; i++) {
num = random(1, 12);
for (int i = 1; i <= num; i++)
{
getline(question3, line);
}
question3.clear();
question3.seekg(0, ios::beg);
testgen << line << endl;
}
question3.close();
testgen.close();
}
int main() {
test();
return 0;
}
这是一种可能的解决方案。使用函数来处理代码的相似部分：
#include <iostream>
#include <string>
#include <fstream>
#include <random>
#include <vector>
#include <tuple>
// From the internet: https://en.cppreference.com/w/cpp/numeric/random/random_device
int random(int from, int to) {
std::random_device random_device;
std::mt19937 generator(random_device());
std::uniform_int_distribution<int> distribution(from, to);
return distribution(generator);
}
std::string readNthLineFromFile(std::ifstream& ifs, int n) {
// Reset file to the beginning
ifs.clear();
ifs.seekg(0, std::ios::beg);
// Default return string in case of error
std::string result{ "\n*** Error while reading a line from the source file\n" };
// If getline fails or ifs is in fail state, the string will be default
for (; std::getline(ifs, result) && (n != 0); n--);
// Give back the desired line
return result;
}
void generateQuestion(std::ifstream& sourceFileStream, std::ofstream& destinationFileStream, int n, const bool twoLines = false) {
// We want to prevent readin the same question again
int oldLineNumber = 0;
// For whatever reason, do this 2 times.
for (size_t i = 0U; i < 2; ++i) {
// If we want to read 2 consecutive lines, then we should not come up with the last kine in the file
if (twoLines & (n > 1)) --n;
// Get a random line number. But no duplicates in the 2 loops
int lineNumber{};
do {
lineNumber = random(1, n);
} while (lineNumber == oldLineNumber);
// For the next loop execution
oldLineNumber = lineNumber;
// Read the random line
std::string line{ readNthLineFromFile(sourceFileStream, lineNumber) };
// And write it to the destination file
destinationFileStream << line << "\n";
// If we want to read to lines in a row
if (twoLines) {
// Read next line
line = readNthLineFromFile(sourceFileStream, ++lineNumber);
// And write it to the destination file
destinationFileStream << line << "\n";
}
}
}
int main() {
const std::string destinationFilename{ "generatedTest.txt" };
const std::string questions1Filename{ "questiondesc.txt" };
const std::string questions2Filename{ "questionmcq.txt" };
const std::string questions3Filename{ "questionanalytical.txt" };
// Here we store the filenames and if one or 2 lines shall be read
std::vector<std::tuple<const std::string, const size_t, const bool>> source{
{ questions1Filename, 12U, false },
{ questions2Filename, 26U, true },
{ questions3Filename, 12U, false }
};
// Open the destination file and check, if it could be opened
if (std::ofstream destinationFileStream(destinationFilename); destinationFileStream) {
// Now open the first source file and generate the questions
for (const std::tuple<const std::string, const size_t, const bool>& t : source) {
// Open source file and check, if it could be opened
if (std::ifstream sourceFileStream(std::get<0>(t)); sourceFileStream) {
generateQuestion(sourceFileStream, destinationFileStream, std::get<1>(t), std::get<2>(t));
}
else {
std::cerr << "\n*** Error. Could not open source file '" << std::get<0>(t) << "'\n";
}
}
}
else {
std::cerr << "\n*** Error: Could not open destination file '" << destinationFilename << "'\n";
}
return 0;
}
我制作了一个测试器 class，我从问题池文本文件中提取问题，然后将其中的随机问题放入 docx 文件中。我想知道为什么我的代码在 docx 文件中给出空白输出。 我的随机函数工作正常。我从三个问题文件中选择两个两个问题。 这是我的代码 - `
void test()
{
string line;
fstream question1("questiondesc.txt",ios::in | ios::out | ios::app);
fstream testgen("GeneratedTest.docx",ios::trunc | ios::in | ios::out);
testgen.open("GeneratedTest.docx");
if(!question1.is_open())
{
question1.open("questiondesc.txt");
}
int i,num;
for (i = 0; i < 2; i++) {
num = random(1,12);
for(int i =1;i<=num;i++)
{
getline(question1,line);
}
question1.clear();
question1.seekg(0, ios::beg);
testgen<<line<<endl;
}
question1.close();
ifstream question2("questionmcq.txt");
if(!question2.is_open())
{
question2.open("questionmcq.txt");
}
for (i = 0; i < 2; i++) {
num = random(1,26);
while(num%2==0)
{
num = random(1,26);
}
for(int i =1;i<=num;i++)
{
getline(question2,line);
}
testgen<<line<<endl;
getline(question2,line);
testgen<<line<<endl;
question2.clear();
question2.seekg(0, ios::beg);
}
question2.close();
ifstream question3("questionanalytical.txt");
if(!question3.is_open())
{
question3.open("questionanalytical.txt");
}
for (i = 0; i < 2; i++) {
num = random(1,12);
for(int i =1;i<=num;i++)
{
getline(question3,line);
}
question3.clear();
question3.seekg(0, ios::beg);
testgen<<line<<endl;
}
question3.close();
testgen.close();
}
您的代码中有错误。我将在下面的列表中将它们显示为评论。此外，我将展示（许多，也许不是最好的）解决方案来解决您的问题。
你应该把你的问题分解成更小的部分并设计更多的功能。那样的话，生活会更轻松。
另外。你应该写评论。如果你写评论，那么你会自己发现问题。
你的代码加上我的备注：
#include <iostream>
#include <fstream>
#include <string>
#include <random>
using namespace std; // NO NEVER USE
int random(int from, int to) {
std::random_device random_device;
std::mt19937 generator(random_device());
std::uniform_int_distribution<int> distribution(from, to);
return distribution(generator);
}
void test()
{
string line; // Line is not initialized an not needed here. Pollutes namespace
fstream question1("questiondesc.txt", ios::in | ios::out | ios::app); // Opening a file with these flags will fail. Use ifstream
fstream testgen("GeneratedTest.docx", ios::trunc | ios::in | ios::out);// Opening a file with these flags will fail. Use ofstream
testgen.open("GeneratedTest.docx"); // File was alread opened and failed. Reopening will not work. It failed alread
if (!question1.is_open()) // Use if "(!question1)" instead. There could be also other error bits
{ // Always check the status of any IO operation
question1.open("questiondesc.txt"); // Will never work. Failer already
}
int i, num; // Variable not initialized and not needed here. Name space pollution
for (i = 0; i < 2; i++) {
num = random(1, 12); // This function was not defined. I redefined it
for (int i = 1; i <= num; i++) // i=1 and i<= reaaly) not i=0 and i<num?
{
getline(question1, line); // Always check status of any IO function
}
question1.clear();
question1.seekg(0, ios::beg);
testgen << line << endl;
}
question1.close(); // The destructor of the fstream will close the file for you
ifstream question2("questionmcq.txt"); // Now you open the file as ifstream
if (!question2.is_open()) // Do check for all possible flags.: If (!question2)
{
question2.open("questionmcq.txt"); // Will not work, if it failed in the first time
}
for (i = 0; i < 2; i++) { // So 2 times
num = random(1, 26);
while (num % 2 == 0) // If numbers are equal
{
num = random(1, 26); // Get an odd number
}
for (int i = 1; i <= num; i++) // Usually from 0 to <num
{
getline(question2, line);
}
testgen << line << endl;
getline(question2, line);
testgen << line << endl;
question2.clear();
question2.seekg(0, ios::beg);
}
question2.close(); // No need to close. Destructor will do it for you
ifstream question3("questionanalytical.txt"); // Now you open the file as ifstream
if (!question3.is_open()) // Wrong check. Check for all flags
{
question3.open("questionanalytical.txt"); // Will not help in case of failure
}
// Now this is the 3rd time with the same code. So, put it into a function
for (i = 0; i < 2; i++) {
num = random(1, 12);
for (int i = 1; i <= num; i++)
{
getline(question3, line);
}
question3.clear();
question3.seekg(0, ios::beg);
testgen << line << endl;
}
question3.close();
testgen.close();
}
int main() {
test();
return 0;
}
这是一种可能的解决方案。使用函数来处理代码的相似部分：
#include <iostream>
#include <string>
#include <fstream>
#include <random>
#include <vector>
#include <tuple>
// From the internet: https://en.cppreference.com/w/cpp/numeric/random/random_device
int random(int from, int to) {
std::random_device random_device;
std::mt19937 generator(random_device());
std::uniform_int_distribution<int> distribution(from, to);
return distribution(generator);
}
std::string readNthLineFromFile(std::ifstream& ifs, int n) {
// Reset file to the beginning
ifs.clear();
ifs.seekg(0, std::ios::beg);
// Default return string in case of error
std::string result{ "\n*** Error while reading a line from the source file\n" };
// If getline fails or ifs is in fail state, the string will be default
for (; std::getline(ifs, result) && (n != 0); n--);
// Give back the desired line
return result;
}
void generateQuestion(std::ifstream& sourceFileStream, std::ofstream& destinationFileStream, int n, const bool twoLines = false) {
// We want to prevent readin the same question again
int oldLineNumber = 0;
// For whatever reason, do this 2 times.
for (size_t i = 0U; i < 2; ++i) {
// If we want to read 2 consecutive lines, then we should not come up with the last kine in the file
if (twoLines & (n > 1)) --n;
// Get a random line number. But no duplicates in the 2 loops
int lineNumber{};
do {
lineNumber = random(1, n);
} while (lineNumber == oldLineNumber);
// For the next loop execution
oldLineNumber = lineNumber;
// Read the random line
std::string line{ readNthLineFromFile(sourceFileStream, lineNumber) };
// And write it to the destination file
destinationFileStream << line << "\n";
// If we want to read to lines in a row
if (twoLines) {
// Read next line
line = readNthLineFromFile(sourceFileStream, ++lineNumber);
// And write it to the destination file
destinationFileStream << line << "\n";
}
}
}
int main() {
const std::string destinationFilename{ "generatedTest.txt" };
const std::string questions1Filename{ "questiondesc.txt" };
const std::string questions2Filename{ "questionmcq.txt" };
const std::string questions3Filename{ "questionanalytical.txt" };
// Here we store the filenames and if one or 2 lines shall be read
std::vector<std::tuple<const std::string, const size_t, const bool>> source{
{ questions1Filename, 12U, false },
{ questions2Filename, 26U, true },
{ questions3Filename, 12U, false }
};
// Open the destination file and check, if it could be opened
if (std::ofstream destinationFileStream(destinationFilename); destinationFileStream) {
// Now open the first source file and generate the questions
for (const std::tuple<const std::string, const size_t, const bool>& t : source) {
// Open source file and check, if it could be opened
if (std::ifstream sourceFileStream(std::get<0>(t)); sourceFileStream) {
generateQuestion(sourceFileStream, destinationFileStream, std::get<1>(t), std::get<2>(t));
}
else {
std::cerr << "\n*** Error. Could not open source file '" << std::get<0>(t) << "'\n";
}
}
}
else {
std::cerr << "\n*** Error: Could not open destination file '" << destinationFilename << "'\n";
}
return 0;
}