Changing the length of a string (allocating memory for characters)

Question

def get_avail_mb(): int

    f: FILE = FILE.open("/proc/meminfo","r")
    s: string = ""
    while s.length < 200 do s += " "
    f.read(s, 200, 1)

    var a = s.split("\n")
    s = a[2]
    t: string = ""
    for var i = 0 to s.length
        if s[i] <= '9' && s[i] >= '0'
            t += s[i].to_string()
    return int.parse(t)/1000

Notice how I allocate the string to 200 charaters with while s.length < 200 do s += " " to read bytes into this string from the file? Is there a better way to set the length of a string to N characters in Genie other than appending space character N times?

Answer 1

Probably the best way is to create a fixed size array as a buffer and cast the buffer to a string. This avoids some C warnings when compiled. Compile with valac --pkg posix example.gs:

[indent=4]
uses
    Posix

init
    print( @"Available memory: $(get_avail_mb()) MB" )

def get_avail_mb():int
    f:FILE = FILE.open("/proc/meminfo","r")
    buffer:uint8[200]
    f.read(buffer, 200, 1)

    result:int = 0
    match_result:MatchInfo
    if ( /^MemAvailable:\s*([0-9]*).*$/m.match(
                                            (string)buffer,
                                            0,
                                            out match_result
                                            ))
        result = int.parse( match_result.fetch( 1 ))/1000
    return result

Alternatively you could try string.nfill ():

[indent=4]
uses
    Posix

init
    print( @"Available memory: $(get_avail_mb()) MB" )

def get_avail_mb():int
    f:FILE = FILE.open("/proc/meminfo","r")
    s:string = string.nfill( 200, ' ' )
    f.read(s, 200, 1)

    result:int = 0
    match_result:MatchInfo
    if ( /^MemAvailable:\s*([0-9]*).*$/m.match(
                                            s,
                                            0,
                                            out match_result
                                            ))
        result = int.parse( match_result.fetch( 1 ))/1000
    return result