Use Ifstream to Read a File String
C++ read binary file is a file Input/Output functioning that is handled by the stream-based interface of the C++ Standard Template Library. You'll need to utilize the std::fstream class for creating a file stream object first, and then the contents of information technology can be read using different methods based on the needs of the solution.
In the following commodity, we volition explore reading files in binary mode, simply besides we'll consider multiple ways of reading the file information itself. Find out the ins and outs of these methods in the upcoming paragraphs.
How To Open up File in Binary Manner C++?
You can open up a file in binary mode by specifying the std::ios_base::binary file open flag equally the parameter to the ::open() role. In this case, we demand to create a file-based stream of type – std::fstream.
Annotation that opening a file using ::binary flag is not sufficient to carry binary read/write operations since it simply affects how the newline characters are translated by the runtime. Then, when a file is opened in ::binary mode, information technology stops converting newline characters from different platforms.
The ::open() function tries to open and associate a real file to the abstract std::fstream object. It takes two parameters, the first of which represents the filename, while the 2d specifies the open flag.
The ::open() part call may neglect for various reasons, so it's always a good idea to verify the status using the ::is_open() built-in method. The following code snippet demonstrates the usage for both functions to open a file in binary manner.
– Code For Open up File in Binary Fashion C++
#include <fstream>
#include <vector>
#include <sstream>using std::cout; using std::cerr;
using std::endl; using std::string;
int main() {
cord filename("newfile.txt");
string file_contents;
std::fstream file;
file.open(filename, std::ios_base::in | std::ios::binary);
if (!file.is_open()) {
file.articulate();
file.open(filename, std::ios_base::out | std::ios_base::binary);
file.close();
file.open(filename, std::ios_base::in | std::ios_base::binary);
cout << "a new file was created!" << endl;
} else {
cout << "file already exists." << endl;
cout << "file was opened on the first try!" << endl;
}
exit(0);
}
How To Read Binary File in C++?
You tin read a binary file using the ::read() method invoked from the std::fstream object. This built-in function extracts characters from the stream and stores them at the address of the char arrow passed to it every bit the commencement argument.
Notice that this function too takes a number of characters that need to be read from the file stream. The side by side case code demonstrates merely a raw usage of the ::read() function.
Generally, reading and writing binary files requires proposed formatting that will brand data persistent in the filesystem or over the communication medium. Furthermore, this demands more delicate usage of STL classes and preferably designing custom classes that are based on std::basic_streambuf. Alternatively, one can utilize 3rd-party C++ libraries that provide the needed functionality.
– Lawmaking For Read Binary File in C++
#include <fstream>
#include <vector>
#include <sstream>
#include <filesystem>using std::cout; using std::cerr;
using std::endl; using std::string;
int main() {
cord filename("newfile.txt");
std::fstream file;
file.open up(filename, std::ios_base::in | std::ios::binary);
if (!file.is_open()) {
file.clear();
file.open(filename, std::ios_base::out | std::ios_base::binary);
file.close();
file.open(filename, std::ios_base::in | std::ios_base::binary);
cout << "a new file was created!" << endl;
} else if (file.skillful()) {
cout << "file already exists." << endl;
cout << "file was opened on the first try!" << endl;
}
auto file_size = std::filesystem::file_size(filename);
char *data = reinterpret_cast<char *>(new int[file_size]);
file.read(data, file_size);
std::string output(data);
cout << output << endl;
exit(0);
}
C++ Read Binary File: Reading the Whole File Into a String
Sometimes, it's useful to read the whole file contents into a string object. The latter can exist accomplished by utilizing the std::ostringstream course and ::rdfbuf() function. To exercise that, we created a split part named FileToString which takes a const std::string reference representing the path to the file to exist read. And then we associated the given file to the std::ifstream object and, finally, extracted the contents using the << operator from the return value of ::rdbuf() function.
The next code sample shows a uncomplicated usage scenario for the to a higher place method. Notice that file contents are inserted into the std::ostringstream object to hands recollect them every bit std::string. Once the contents are inserted, the ::str() built-in function tin can exist invoked to return a copy of the underlying string.
– Code For Read File Into a Cord in C++
#include <fstream>
#include <vector>
#include <sstream>
#include <filesystem>using std::cout; using std::cerr;
using std::endl; using std::string;
using std::ifstream; using std::ostringstream;
string FileToString(const string& path) {
auto ss = ostringstream{};
ifstream input_file(path);
if (!input_file.is_open()) {
cerr << "[ERROR] could non open up file '" << path << "'.\n";
exit(EXIT_FAILURE);
}
ss << input_file.rdbuf();
render ss.str();
}
int master() {
string file_path("/dwelling house/tmp.txt");
string file_data_string = FileToString(file_path);
cout << file_data_string << endl;
exit(0);
}
– Using C++ Read Bytes From File
Alternatively, you can use the std::istreambuf_iterator iterator that reads successive characters from the object std::basic_streambuf object for which information technology was constructed. This method implements the FileToString office that constructs the std::string object past passing the std::basic_streambuf, which is based on the file stream object. Similar to the previous solution, the FileToString role takes a file path reference to std::string equally the only parameter. Note that these methods should be utilized only on text streams.
– Code For C++ Read Bytes From File
#include <fstream>
#include <vector>
#include <sstream>
#include <filesystem>using std::cout; using std::cerr;
using std::endl; using std::string;
using std::ifstream; using std::ostringstream;
cord FileToString(const string& path) {
ifstream input_file(path);
if (!input_file.is_open()) {
cerr << "[ERROR] could not open file '" << path << "'.\due north";
go out(EXIT_FAILURE);
}
render string((std::istreambuf_iterator<char>(input_file)), std::istreambuf_iterator<char>());
}
int master() {
string file_path("/home/tmp.txt");
string file_data_string = FileToString(file_path);
cout << file_data_string << endl;
exit(0);
}
Read File Contents Byte by Byte in C++
C++ reddish file byte past byte can be achieved using the C standard library facilities for I/O. In our case, we are going to employ the fread() role to read binary stream data and and so print bytes in hexadecimal notation.
This solution is demonstrated in the following code snippet, where you would just need to change a filename that should be attainable to the program. If your file is located in a unlike location than the compiled program, then you should specify the path to it.
Notice that this code case also utilizes fopen() function from the C standard library to think FILE* object – afterward to be passed as an argument for the fread() function. Moreover, stat() Unix system call is used to retrieve the size of the file. Finally, we use printf() to output contents byte by bytes to the terminal formatted in hexadecimal annotation.
Note that the memory should be allocated dynamically for the array where the file contents are saved, and you should be aware of the allocation errors if the file to exist read is relatively huge. You might too choose to map files into the retention using platform-specific API, east.g., mmap() in POSIX systems.
– Code For C++ Read File Byte by Byte
#include <sys/stat.h>
#include <unistd.h>
#include <unistd.h>using std::cout; using std::cerr;
using std::endl; using std::string;
int main() {
cord filename("filename");
auto in_file = fopen(filename.c_str(), "rb");
if (!in_file) {
perror("fopen");
exit(EXIT_FAILURE);
}
struct stat sb{};
if (stat(filename.c_str(), &sb) == -one) {
perror("stat");
go out(EXIT_FAILURE);
}
u_char* file_contents = new u_char[sb.st_size];
fread(file_contents, sb.st_size, i, in_file);
for (int i = 0; i < sb.st_size; ++i) {
printf("%02X ", file_contents[i]);
if (i % 10 == 0 && i != 0){
cout << '\n';
}
}
delete [] file_contents;
exit(0);
}
Cardinal Takeaways
In this commodity, we covered some basic techniques about reading binary files C++, and even though binary file manipulations normally involve some type of formatting, you might need to extend these methods with custom classes. Here are some recommendations for reading a binary file in C++:
- std::ios_base::binary open flag is not enough to comport operations on binary file streams
- Don't apply stream insertion/extraction (<< >>) operators when dealing with binary files
- Amend construct custom std::basic_streambuf derived classes than utilize ::read/::write functions
- Make utilise of extensively tested third-party libraries if a custom implementation seems as well complex for your skills
At present you should exist able to move on to some binary file reading do problems. Try tinkering with unproblematic compiled C++ program files which are binary formatted, and and then you tin experiment with more than circuitous formats.
- Author
- Recent Posts
Position Is Everything: Your Go-To Resource for Acquire & Build: CSS,JavaScript,HTML,PHP,C++ and MYSQL.
Source: https://www.positioniseverything.net/cpp-read-binary-file
Post a Comment for "Use Ifstream to Read a File String"