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The CS1010 I/O Library

To help students get started with C programming without worrying too much about the details and pitfalls of using printf and scanf, we provide a simple-to-use library to read and write integers, floating point numbers, and strings.

The libraries are pre-installed in CS1010 programming environments, with cs1010.h located under ~cs1010/include and libcs1010.a located under ~cs1010/lib.

Installing the Library

If you want to install the libraries on your own version of Ubuntu, do the following:

  1. To get an updated copy of the library, clone it from its git repo on GitHub with the command:
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git clone https://github.com/nus-cs1010/libcs1010.git

It is recommended you do this in your home directory.

You should see an output similar to: 

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Cloning into 'libcs1010'...
remote: Counting objects: 6, done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 6 (delta 0), reused 0 (delta 0), pack-reused 0
Unpacking objects: 100% (6/6), done.

After that, you should see a subdirectory libcs1010 created in your current directory. Inside, there should be a file called Makefile, and two subdirectories called include and src.

  1. To compile the library, run
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make

This should compile the file src/cs1010.c and create a static C library named libcs1010.a under the lib directory.

Using the Library

To use the CS1010 I/O library, you should #include the file cs1010.h, like this:

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#include "cs1010.h"

at the top of your C program.

Linking

The CS1010 I/O library is provided as the file libcs1010.a. To link to the library, you need to compile with -lcs1010. Usually, you need to specify where you can find cs1010.h with the -I flag, and libcs1010.a with the -L flag. Assuming that you are compiling in another subdirectory under your home and libcs1010 are located under your home directory, the header file and the library file are in ../libcs1010/include and ../libcs1010/lib respectively.

So you compile using the command line:

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clang -I../libcs1010/include -L../libcs1010/lib hello.c -lcs1010

Of course if your header and library files are located in another directory that is not ../libcs1010/include and ../libcs1010/lib, you should change the command above accordingly.

Although it is a long string to type, you should type it once and use up arrow in bash to go back to this command over-and-over again. For advanced students, we suggest that you put this in a shell script so that you just need to run the shell script to compile the program. We have also automate this for you for your assignments and exercises using the make command.

Reading of a Single Value

The CS1010 library supports reading of long value, double value, and strings (both space-separated words and newline-separated lines) from the standard input. For long and double. The relevant methods are:

  • long cs1010_read_long()
    Returns a long value from the standard input. An error message will be printed (to stderr) if the input sequence is not a valid long value -- in which case the value LONG_MAX will be returned. Example: 

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    long year = cs1010_read_long();

  • double cs1010_read_double()
    Returns a double value from the standard input. An error message will be printed (to stderr) if the input sequence is not a valid double value -- in which case the value DBL_MAX will be returned. Example: 

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    double cap = cs1010_read_double();

  • char* cs1010_read_word()
    Returns a char * pointing to the next white-space-separated string from the standard input. A white-space character is defined based on the standard C function isspace() and includes the space , tab \t, and newline \n character. Returns NULL if there is an error. If the returned value is non-NULL, the caller is responsible for freeing the memory allocated by calling free.

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    char* word = cs1010_read_word();
// use word to do something
 :
 :
free(word);

  • char* cs1010_read_line()
    Returns a char * pointing to the next new-line-separated string from the standard input. The string returns from cs1010_read_line() includes the newline character (if one is found). Returns NULL if there is an error. If the returned value is non-NULL, the caller is responsible for freeing the memory allocated by calling free. 

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    char* line = cs1010_read_line();
// use line to do something
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free(line);

Reading of Multiple Values

Update to API

In September AY20/21, we updated the API to take in a long instead of an int for cs1010_read_*_array functions, to be consistent with the rest of the CS1010 materials.

The CS1010 library also supports reading of multiple values.

  • long* cs1010_read_long_array(long k)
    Returns k numbers of long values read from the standard input stored in an array. An error message will be printed (to stderr) for each input that is not a valid long value -- in which case the value LONG_MAX will be populated in the corresponding array element. Returns NULL if there is a memory allocation error. If the returned value is non-NULL, the caller is responsible for freeing the memory allocated by calling free. 

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    long* values = cs1010_read_long_array(10);
if (values != NULL) {
  // Do something with array values
   :
   :
  free(values);
}

  • double* cs1010_read_double_array(long k)
    Returns k numbers of double values read from the standard input stored in an array. An error message will be printed (to stderr) for each input that is not a valid double value -- in which case the value DBL_MAX will be populated in the corresponding array element.
    Returns NULL if there is a memory allocation error. If the returned value is non-NULL, the caller is responsible for freeing the memory allocated by calling free. 

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    double* values = cs1010_read_double_array(10);
if (values != NULL) {
  // Do something with array values
   :
   :
  free(values);
}

  • char** cs1010_read_word_array(long k)
    Returns k white-space-separated words read from the standard input stored in an array. The notion of "word" is the same to cs1010_read_word().
    Returns NULL if there is a memory allocation error. If the returned value is non-NULL, the caller is responsible for freeing the memory allocated for each word and for the whole array by calling free. 

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    char** words = cs1010_read_word_array(10);
if (words != NULL) {
  // Do something with array words
   :
   :
  for (long i = 0; i < 10; i += 1) {
    free(words[i]);
  }
  free(words);
}

  • char** cs1010_read_line_array(long k)
    Returns k new-line-separated words read from the standard input stored in an array. The notion of line is the same to cs1010_read_line().
    Returns NULL if there is a memory allocation error. If the returned value is non-NULL, the caller is responsible for freeing the memory allocated for each line and for the whole array by calling free. 

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    char** lines = cs1010_read_line_array(10);
if (lines != NULL) {
  // Do something with array lines
   :
   :
  for (long i = 0; i < 10; i += 1) {
    free(lines[i]);
  }
  free(lines);
}

Printing of a Single Value

The CS1010 library provides a few convenince functions to format and print long and double values to the standard output.

  • void cs1010_print_long(long value) and void cs1010_println_long(long value)
    Print value to the standard output (with printf format %ld).
    The cs1010_println_long version prints a newline after the value. 

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      long x;
    :
  cs1010_print_long(x);

  • void cs1010_print_double(double value) and void cs1010_println_double(double value)
    Print value to the standard output (with printf format %.4f). The cs1010_println_double version prints a newline after the value. 

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      double x;
    :
  cs1010_println_double(x);

  • void cs1010_print_string(char *str) and void cs1010_println_string(char *str)
    Print a given string str to the standard output. These functions are provided for completeness and is a simple wrapper around printf(str) and printf("%s\n", str) repsectively. 

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      cs1010_println_string("hello world!");

Printing single character

There is no cs1010_print_char method. You can use putchar from the C standard library for this purpose.

Clearing screen

The CS1010 library provides a function to clear your screen. 

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  cs1010_clear_screen();