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# file io

# ifstream

# ofstream

# fstream

#include "common.hpp"

void ios_write_fail(std::string path) {

throw std::ios_base::failure("Error: Could not write to file: " + path);

}

void ios_read_fail(std::string path) {

throw std::ios_base::failure("Error: Could not read file: " + path);

}

/**

Read entire file into a string at once.

void read_file(std::ifstream &ifs, std::string &data_read) {

ifs.seekg(0, std::ios::end);

size_t size = ifs.tellg();

data_read.resize(size);

ifs.seekg(0);

ifs.read(&data_read[0], size);

ifs.close();

}

int main() {

std::string path("fileio.tmp");

std::string data("ab\n\nc\n");

// Write to file.

{

std::ofstream ofs(path);

if (ofs) {

ofs << data;

ofs.close();

} else {

ios_write_fail(path);

}

# Read entire file at once

http://stackoverflow.com/questions/2602013/read-whole-ascii-file-into-c-stdstring

Best way seems to be to get file size, allocate, and read manually.

{

std::ifstream ifs(path);

if (ifs) {

std::string data_read;

read_file(ifs, data_read);

assert(data_read == data);

} else {

ios_read_fail(path);

}

# Copy file to another

# cp

# rdbuf

http://stackoverflow.com/questions/2141749/what-does-ifstreamrdbuf-actually-do

{

std::string data = "abc\ndef\n";

std::string src_path = "src.tmp";

std::string dst_path = "dst.tmp";

// Create input file.

{

std::ofstream src(src_path, std::ios::binary);

src << data;

// 2 times 4 Gb.

//for (int i = 0; i < 2; i++) {

//for (int j = 0; j < 0xFFFFFFFF; j++) {

//src << std::hex << j;

//}

src.close();

}

// Copy.

std::ifstream src(src_path, std::ios::binary);

std::ofstream dst(dst_path, std::ios::binary);

dst << src.rdbuf();

src.close();

dst.close();

// Check copy.

{

std::ifstream dst(dst_path, std::ios::binary);

std::string data_read;

read_file(dst, data_read);

assert(data_read == data);

src.close();

}

# Compare two files larger than memory.

TODO is there an easier way than reading each?

{

}

// # Append to file

{

std::ofstream ofs(path);

if (ofs) {

ofs << data;

ofs.close();

} else {

ios_write_fail(path);

}

# open

# Reopen

Can be used to reopen ofstream with new properties.

Also consider clearing error flags if there can be any.

//ofs.clear()

ofs.open(path, std::ios::app);

if (ofs) {

ofs << data;

ofs.close();

} else {

ios_write_fail(path);

}

std::ifstream ifs(path);

if (ifs) {

std::string data_read;

read_file(ifs, data_read);

assert(data_read == data + data);

} else {

ios_read_fail(path);

}

# binary io

Use ios::binary, and the binary functions write and read.

{

// TODO

//std::string path("binary.tmp");

//std::vector<int> data{0x123, 0x456};

//std::vector<int>::size_type size = data.size();

//std::vector<int> data_read(size);

//std::ofstream ofs(path, std::ios::binary);

//if (ofs) {

//ofs.write(&data[0], size);

//ofs.close();

//} else {

//ios_write_fail(path);

//}

//std::ifstream ifs(path);

//if (ifs) {

//std::string data_read;

//read_file(ifs, data_read);

//assert(data_read == data);

//} else {

//ios_read_fail(path);

//}

}

# error handling

# is_open vs bool cast

`is_open` false implies `operator bool()` false, but the converse is false: `operator bool()` is more strict.

<http://stackoverflow.com/questions/14920457/c-difference-between-casting-ifstream-to-bool-and-using-ifstreamis-open>

IO functions do not raise exceptions by default, but may be turned on.

The best standard exception to raise is probably `std::ios_base::failure`.

Relevant standard exceptions:

http://en.cppreference.com/w/cpp/io/ios_base/failure

SO thread:

http://stackoverflow.com/questions/9670396/exception-handling-and-opening-a-file

{

std::string path("i_dont_exist.tmp");

std::ifstream ifs(path);

if (ifs) {

assert(false);

} else {

try {

//throw std::ios_base::failure("Error: Could not write to file: " + path);

} catch (std::ios_base::failure e) {

std::clog << e.what() << std::endl;

}

// # ios::in: flag automatically set for ifstream, but not fstream

//http://stackoverflow.com/questions/7463410/is-iosin-needed-for-ifstreams-opened-in-binary-mode

}

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