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Engineering LibreTexts

7.5: Loading an Array from a Text File

  • Page ID
    10704
  • Overview

    Loading an array from a text file requires several steps, including: opening the file, reading the records, parsing (splitting) the records into fields, adding the fields to an array, and closing the file. The file may be read all at once and then parsed, or processed line by line. The array must either be at least as large as the number of records in the file, or must be generated dynamically.

    Discussion

    Loading an array from a file presents an interesting dilemma. The problem resolves around how many elements you should plan for in the array. Let’s say 100, but what if the file has fewer or more than 100 values. How can the program handle it correctly?

    Either:

    1. Read the file and count the number of records.
    2. Create a static array of that size.
    3. Read the file again and add each record to the array.

    Or:

    1. Read the file and dynamically add the records to the array.

    Processing Records

    There are two options for file processing:

    1. Read the entire file into memory, split the records and then process each record.
    2. Read the file line by line and process one record at a time.

    Which of these approaches is better will depend on the size of the file and the types of file and string processing supported by your programming language. Reading the entire file at once may be faster for small files. Very large files must be processed line by line.

    Processing Fields

    Processing fields requires splitting records based on the given file format. For example, a comma-separated-values file might be formatted as:

    Celsius,Fahrenheit
    0.0,32.0
    1.0,33.8
    2.0,35.6
    

    The first line contains field names separated by commas. Following lines contain a value for each of the fields, separated by commas. Note that all text file input is strings. Each line must be split on the field separator (comma), and then numeric fields must be converted to integer or floating point values for processing.

    Pseudocode

    Static Array Processing

    Open file
    Read header
    While Not End-Of-File
        Read line
        Increment record count
    Close file
    
    Declare array with length based on record count
    Read Header
    While Not End-Of-File
        Read line
        Split line into field(s)
        Convert numeric values to numeric data types
        Add field(s) to array or parallel arrays
    Close file
    

    Dynamic Array Processing

    Declare empty array
    Open file
    Read Header
    While Not End-Of-File
        Read line
        Split line into field(s)
        Convert numeric values to numeric data types
        Add field(s) to array or parallel arrays
    Close file
    

    Key Terms

    dynamic memory
    Aka stack created memory associated with local scope.
    static memory
    Aka data area memory associated with global scope.