libcs50 - CS50 library for C

Installation

Ubuntu

$ curl -s https://packagecloud.io/install/repositories/cs50/repo/script.deb.sh | sudo bash
$ sudo apt install libcs50

Fedora

$ curl -s https://packagecloud.io/install/repositories/cs50/repo/script.rpm.sh | sudo bash
$ dnf install libcs50

From Source (Linux and Mac)

  1. Download the latest release from https://github.com/cs50/libcs50/releases
  2. Extract libcs50-*.*
  3. cd libcs50-*
  4. sudo make install

Troubleshooting

If when compiling your program, you see:

/usr/bin/ld: cannot find -lcs50:
Add export LIBRARY_PATH=/usr/local/lib to your .bashrc.
fatal error: 'cs50.h' file not found:
Add export C_INCLUDE_PATH=/usr/local/include to your .bashrc.
cannot open shared object file: No such file or directory:
Add export LD_LIBRARY_PATH=/usr/local/lib to your .bashrc.

Usage

Note

To use these functions, make sure to include #include <cs50.h> atop your file and compile with the -lcs50 flag.

string

Type representing a C string. Aliased to char *.

Example usage:

string s = "hello, world!";
void eprintf(const char *format, ...)
Parameters:
  • format – the printf()-like format string used to display the prompt
  • ... – values to be substituted into the format string a la printf()

Prints an error message formatted like printf() to standard error, prefixing it with file and line number from which the function was called.

Example usage:

int main(void)
{
    eprintf("This line of code should be executed\n");

    int i;
    for (i = 0; i < 50; i++)
    {
        printf("i is %d\n", i);
    }

    eprintf("Expected i to be 49 but it is actually %d\n", i);
}
char get_char(const char *format, ...)
Parameters:
  • format – the printf()-like format string used to display the prompt
  • ... – values to be substituted into the format string a la printf()
Returns:

the char equivalent to the line read from stdin, or CHAR_MAX on error

Prompts user for a line of text from standard input and returns the equivalent char; if text does not represent a single char, user is reprompted.

Example usage:

#include <stdio.h>
#include <cs50.h>

int main(void)
{
    // attempt to read character from stdin
    char c = get_char("Enter char: ");

    // ensure character was read successfully
    if (c == CHAR_MAX)
    {
        return 1;
    }

    char next = get_char("You just entered %c. Enter another char: ", c);

    if (next == CHAR_MAX)
    {
        return 1;
    }

    printf("The last char you entered was %c\n", next);
}
double get_double(const char *format, ...)
Parameters:
  • format – the printf()-like format string used to display the prompt
  • ... – values to be substituted into the format string a la printf()
Returns:

the double equivalent to the line read from stdin in [DBL_MIN, DBL_MAX), as precisely as possible, or DBL_MAX on error

Prompts user for a line of text from standard input and returns the equivalent double; if text does not represent a double or would cause overflow or underflow, user is reprompted.

Example usage:

double divide_doubles(void)
{
    // read double from stdin
    double d = get_double("Enter a double: ");

    // make sure we read one successfully
    if (d == DBL_MAX)
    {
        return DBL_MAX;
    }

    double e = get_double("What do you want to divide %lf by? ", d);

    // make sure we don't divide by zero
    if (e == DBL_MAX || e == 0.0)
    {
        return DBL_MAX;
    }

    return i / j;
}
int get_int(const char *format, ...)
Parameters:
  • format – the printf()-like format string used to display the prompt
  • ... – values to be substituted into the format string a la printf()
Returns:

the int equivalent to the line read from stdin in [INT_MIN, INT_MAX) or INT_MAX on error

Prompts user for a line of text from standard input and returns the equivalent int; if text does not represent an int or would cause overflow, user is reprompted.

Example usage:

#include <cs50.h>

...

// Returns the sum of two ints read from stdin, or INT_MAX if there was an error.
int add_ints(void)
{
    // read int from stdin
    int i = get_int("Enter an int: ");

    // make sure we read one successfully
    if (i == INT_MAX)
    {
        return INT_MAX;
    }

    int j = get_int("What do you want to add %d to? ", i);

    if (j == INT_MAX)
    {
        return INT_MAX;
    }

    return i + j;
}
float get_float(const char *format, ...)
Parameters:
  • format – the printf()-like format string used to display the prompt
  • ... – values to be substituted into the format string a la printf()
Returns:

the float equivalent to the line read from stdin in [FLT_MIN, FLT_MAX), as precisely as possible, or FLT_MAX on error

Prompts user for a line of text from standard input and returns the equivalent float; if text does not represent a float or would cause overflow or underflow, user is reprompted.

Example usage:

// Returns the product of two floats, or FLT_MAX on error.
float multiply_floats(void)
{
    // read float from stdin
    float f = get_float("Enter a float: ");

    // make sure we read one successfully
    if (f == FLT_MAX)
    {
        return FLT_MAX;
    }

    float g = get_float("What do you want to multiply %f by? ", f);

    if (g == FLT_MAX)
    {
        return FLT_MAX;
    }

    return f * g;
}
long get_long(const char *format, ...)
Parameters:
  • format – the printf()-like format string used to display the prompt
  • ... – values to be substituted into the format string a la printf()
Returns:

the long equivalent to the line read from stdin in [LONG_MIN, LONG_MAX) or LONG_MAX on error

Prompts user for a line of text from standard input and returns the equivalent long; if text does not represent an int or would cause overflow, user is reprompted.

Example usage:

#include <cs50.h>

...

// Returns the difference of two longs read from stdin, or LONG_MAX if there was an error.
long subtract_longs(void)
{
    // read long from stdin
    long i = get_long("Enter a long: ");

    // make sure we read one successfully
    if (i == LONG_MAX)
    {
        return LONG_MAX;
    }

    long j = get_long("What do you want to subtract from %ld? ", i);

    if (j == LONG_MAX)
    {
        return LONG_MAX;
    }

    return i - j;
}
char *get_string(const char *format, ...)
param format:the printf()-like format string used to display the prompt
param …:values to be substituted into the format string a la printf()
returns:the read line as a string sans line endings, or NULL on EOF.

Prompts user for a line of text from standard input and returns it as a string (char *), sans trailing line ending. Supports CR (\r), LF (\n), and CRLF (\r\n) as line endings. Stores string on heap, but library’s destructor frees memory on program’s exit.

Example usage:

int main(void)
{
    string s = get_string("Enter string: ");

    // ensure string was read
    if (s == NULL)
    {
        return 1;
    }

    string next = get_string("You just entered %s. Enter a new string: ", s);

    if (next == NULL)
    {
        return 1;
    }

    printf("Your last string was %s\n", next);
}