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)

Download the latest release from https://github.com/cs50/libcs50/releases

Extract libcs50-*.*

cd libcs50-*

sudo make install

Environment Variables

For parity with Visual Studio Code for CS50 and cli50, you may want to set these environment variables:

CC="clang"
CFLAGS="-ferror-limit=1 -gdwarf-4 -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-gnu-folding-constant -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wno-unused-but-set-variable -Wshadow"
LDLIBS="-lcrypt -lcs50 -lm"

Makefile

Alternatively, if using a Makefile to compile a program (e.g., foo) from multiple files (e.g., foo.c and bar.c), you could structure it as follows. But be sure the last line begins with an actual tab character (\t), not spaces.

CC= clang
CFLAGS = -ferror-limit=1 -gdwarf-4 -ggdb3 -O0 -std=c11 -Wall -Werror -Wextra -Wno-gnu-folding-constant -Wno-sign-compare -Wno-unused-parameter -Wno-unused-variable -Wno-unused-but-set-variable -Wshadow
LDLIBS = -lcrypt -lcs50 -lm

EXE = foo

SRCS = foo.c bar.c
OBJS = $(SRCS:.c=.o)


$(EXE): $(OBJS)
     $(CC) $(CFLAGS) -o $@ $(OBJS) $(LDLIBS)

Usage

Note

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

type string

Type representing a C string. Aliased to char *.

Example usage:

string s = "hello, world!";

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);
}

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.