C++使用ifstream读取文件内容的示例详解

测试文件如下内容：myfile.txtFry:OneJilliondollars.[Everyonegasps.]Auctioneer:Sir,thatsnotanumber.数据读...

测试文件如下内容：myfile.txt

Fry: One Jillion dollars.
 [Everyone gASPs.]
 Auctioneer: Sir, that's not a number.
 数据读取， 测试 。

C++中使用ifstream类实现读文件操作，代码如下：

实现了：

1、以行读取文件

2、逐个词读取文件

3、文件名正确性检测

#include <IOStream>
#include <fstream>
#include <string>

using namespace std;

//读取整个文件内容到char array数组中去
void fileReadAllToCharArray()
{
std::ifstream file;
//以只读方式打开文件
file.open("myfile.txt", std::ios::in);

//指针定位到文件末尾
file.seekg(0, std::ios::end);
int fileLength = file.tellg();

//指定定位到文件开始
file.seekg(0, std::ios::beg);

cout << "fileLength:" << fileLength << endl;
char* buffer = new char[fileLength + 1];
file.read(buffer, fileLength);
buffer[fileLength] = '\0';
string contents = buffer;
cout << "contents:" << contents << endl;

if (buffer) {
delete[] buffer;
}
file.close();
}

//读取方式:逐行读取Line by Line, 将行读入字符数组, 行之间用回车换行区分
void fileReadToCharArray()
{
std::ifstream file("myfile.txt");

constexpr int LINE_LENGTH = 100;
char str[LINE_LENGTH];

int lineNum = 0;
while (file.getline(str, LINE_LENGTH))
{
cout << "Read from line[" << ++lineNum << "] :"<<str<<endl;
}
cout << "file has line:" << lineNum << endl;
}

//读取方式:逐行读取Line by Line, 将行读入string, 行之间用回车换行区分
void fileReadToString()
{
std::ifstream file("myfile.txt");

int lineNum = 0;
string str;
while (getline(file, str)) {
cout << "Read Data on Line:[" << ++lineNum<<"] :" << str <<endl;
}
cout << "file has line:" << lineNum << endl;
}

//读取方式：逐词读取Word by Word，词之间用空格划分
void fileReadwbW()
{
std::ifstream file("myfile.txt");
string s;
while (file >> s)
{
cout << "Read From File[" << s <<"]"<<endl;
}
}

//带检测文件名功能
void fileReadWithErrCheck()
{
string fileName = "file .dat";
std::ifstream fin(fileName.c_str());
if (!fin) {
cout << "Error Opening file:[" << fileName << "]" << " for input " << endl;
exit(-1);
}
}
int main()
{
#if  0
char data[100];

ofstream outfile;
outfile.open("myfile.txt", ios::out | ios::trunc);

cout << "enter your name: ";
//cin.getline(data, 100);
outfile << "hello world"<<endl;

ifstream infile;
infile.open("myfile.txt", ios::in);
cout << "read file from myfile.txta" << endl;
string readData;
infile >> readData;
std::cout << "data:" << readData << endl;
outfile.close();
#endif

//读取整个文件内容到char array数组中去
fileReadAllToCharArray();
std::cout << "-----------------" << endl;

//逐行读取Line by Line
fileReadToCharArray();
std::cout << "-----------------" << endl;

//文件逐词读取Word by Word
fileReadWbW();
std::cout << "-----------------" << endl;

//逐行读取Line by Line, 将行读入string分
fileReadToString();

//带检测文件名功能
fileReadWithErrCheck();
std::cout << "-----------------" << endl;
}

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