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Programming-Idioms

  • Python
  • Scala
  • C++

Idiom #58 Extract file content to a string

Create the string lines from the content of the file with filename f.

#include <sstream>
std::string fromFile(std::string _f)
{
    std::ifstream t(_f);
    t.seekg(0, std::ios::end);
    size_t size = t.tellg();
    std::string buffer(size, ' ');
    t.seekg(0);
    t.read(&buffer[0], size); 
}
lines = open(f).read()

For more complicated file operations, use a context manager with with
with open(f) as fo:
    lines = fo.read()

The with statement creates a contextmanager, which automatically handles closing the file for you when you're done. Without this, you should be manually closing file objects so that you are not relying on the garbage collector to do this for you.
import scala.io.Source
val lines = Source.fromFile(filename).getLines().mkString("\n")
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
int err = 0;
int fd = 0;
void * ptr = NULL;
struct stat st;
if ((fd = open (f, O_RDONLY))
&& (err = fstat (fd, &st)) == 0
&& (ptr = mmap (NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0)) != -1) {
    const char * lines = ptr;
    puts (lines);
    munmap (ptr, st.st_size);
    close (fd);
}

Mapping the whole file into the process address space avoids allocating memory.
New implementation...
< > ⌨
programming-idioms.org 
std::string fromFile(std::string _f)
{
    std::ifstream t(_f);
    t.seekg(0, std::ios::end);
    size_t size = t.tellg();
    std::string buffer(size, ' ');
    t.seekg(0);
    t.read(&buffer[0], size); 
}
lines = open(f).read()
with open(f) as fo:
    lines = fo.read()
val lines = Source.fromFile(filename).getLines().mkString("\n")
int err = 0;
int fd = 0;
void * ptr = NULL;
struct stat st;
if ((fd = open (f, O_RDONLY))
&& (err = fstat (fd, &st)) == 0
&& (ptr = mmap (NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd, 0)) != -1) {
    const char * lines = ptr;
    puts (lines);
    munmap (ptr, st.st_size);
    close (fd);
}
FILE *file;
size_t len=0;
char *lines;
assert(file=fopen(f,"rb"));
assert(lines=malloc(sizeof(char)));

while(!feof(file))
{
	assert(lines=realloc(lines,(len+0x1000)*sizeof(char)));
	len+=fread(lines,1,0x1000,file);
}

assert(lines=realloc(lines,len*sizeof(char)));

(def lines (slurp f))
string lines = File.ReadAllText(f);
string lines = cast(string) read(f, size_t.max);
auto lines = f.readText;
var lines = new File(f).readAsStringSync();
lines = File.read!(f)
{ok, Lines} = file:read_file(F).
program p
   character(len=:),allocatable :: s
   open(unit=10,file='myfile',access='stream')
   inquire(10,size=i)
   allocate(character(len=i) :: s)
   read(10)(s(j:j),j=1,i)
   write(*,*)s
end program p

b, err := os.ReadFile(f)
if err != nil {
	// Handle error...
}
lines := string(b)
do lines <- readFile f; putStr lines
fs.readFile(f, (err, lines) => {
    if (err) {
        // Handle error...
    }

    // Work with `lines` here.
}
File F = new File(f);
try (Scanner s = new Scanner(F)) {
    s.useDelimiter("\\R");
    String n = lineSeparator(),
           lines = s.tokens()
                    .collect(joining(n));
}
byte[] encoded = Files.readAllBytes(Paths.get(f));
String lines = new String(encoded, StandardCharsets.UTF_8);
File(f).readText()
(defvar *lines*
   (with-open-file (stream f)
      (let ((contents (make-string (file-length stream))))
            (read-sequence contents stream)
      :return contents)))
(with-open-file (stream f)
  (uiop:slurp-stream-string stream))
lines = io.input(f):read('a')
NSString *lines=[NSString stringWithContentsOfFile:f encoding:e error:NULL];

$lines = file_get_contents('f');
if ($lines === false) {
    // handle error...
}
var
 _lines, _f: String;
 SL: TStringList;
begin
  SL := TStringList.Create;
  SL.LoadFromFile(_f);
  _lines := SL.Text;
  SL.Free;
end;
open my $fh, '<', $f;
my $lines = do { local $/; <$fh> };
close $fh;
lines = File.read(f)
let mut file = File::open(f)?;
let mut lines = String::new();
file.read_to_string(&mut lines)?;
let lines = fs::read_to_string(f).expect("Can't read file.");
| lines |
lines := f asFilename readStream upToEnd.
Dim lines = IO.File.ReadAllText(f)