In this project I will develop my own implementation of the string.h library in C programming language with some additions (with my own implementation of sprintf and sscanf functions).
The C programming language has a set of functions implementing operations on strings (character strings and byte strings) in its standard library. Various operations, such as copying, concatenation, tokenization and searching are supported. For character strings, the standard library uses the convention that strings are null-terminated: a string of n characters is represented as an array of n + 1 elements, the last of which is a "NULL" character.
The only support for strings in the programming language proper is that the compiler translates quoted string constants into null-terminated strings.
| No. | Variable | Description |
|---|---|---|
| 1 | size_t | This is the unsigned integral type and is the result of the sizeof keyword. |
| No. | Macro | Description |
|---|---|---|
| 1 | NULL | This macro is the value of a null pointer constant. |
| No. | Function | Description |
|---|---|---|
| 1 | void *memchr(const void *str, int c, size_t n) | Searches for the first occurrence of the character c (an unsigned char) in the first n bytes of the string pointed to, by the argument str. |
| 2 | int memcmp(const void *str1, const void *str2, size_t n) | Compares the first n bytes of str1 and str2. |
| 3 | void *memcpy(void *dest, const void *src, size_t n) | Copies n characters from src to dest. |
| 4 | void *memset(void *str, int c, size_t n) | Copies the character c (an unsigned char) to the first n characters of the string pointed to, by the argument str. |
| 5 | char *strncat(char *dest, const char *src, size_t n) | Appends the string pointed to, by src to the end of the string pointed to, by dest up to n characters long. |
| 6 | char *strchr(const char *str, int c) | Searches for the first occurrence of the character c (an unsigned char) in the string pointed to, by the argument str. |
| 7 | int strncmp(const char *str1, const char *str2, size_t n) | Compares at most the first n bytes of str1 and str2. |
| 8 | char *strncpy(char *dest, const char *src, size_t n) | Copies up to n characters from the string pointed to, by src to dest. |
| 9 | size_t strcspn(const char *str1, const char *str2) | Calculates the length of the initial segment of str1 which consists entirely of characters not in str2. |
| 10 | char *strerror(int errnum) | Searches an internal array for the error number errnum and returns a pointer to an error message string. You need to declare macros containing arrays of error messages for mac and linux operating systems. Error descriptions are available in the original library. Checking the current OS is carried out using directives. |
| 11 | size_t strlen(const char *str) | Computes the length of the string str up to but not including the terminating null character. |
| 12 | char *strpbrk(const char *str1, const char *str2) | Finds the first character in the string str1 that matches any character specified in str2. |
| 13 | char *strrchr(const char *str, int c) | Searches for the last occurrence of the character c (an unsigned char) in the string pointed to by the argument str. |
| 14 | char *strstr(const char *haystack, const char *needle) | Finds the first occurrence of the entire string needle (not including the terminating null character) which appears in the string haystack. |
| 15 | char *strtok(char *str, const char *delim) | Breaks string str into a series of tokens separated by delim. |
- int sscanf(const char *str, const char *format, ...) - reads formatted input from a string.
- int sprintf(char *str, const char *format, ...) - sends formatted output to a string pointed to, by str.
where:
- str − This is the C string that the function processes as its source to retrieve the data;
- format − This is the C string that contains one or more of the following items: Whitespace character, Non-whitespace character and Format specifiers. A format specifier for print functions follows this prototype: %[flags][width][.precision][length]specifier. A format specifier for scan functions follows this prototype: %[*][width][length]specifier.
| No. | Specifier | sprintf output | sscanf output |
|---|---|---|---|
| 1 | c | Character | Character |
| 2 | d | Signed decimal integer | Signed decimal integer |
| 3 | i | Signed decimal integer | Signed integer (may be decimal, octal or hexadecimal) |
| 4 | e | Scientific notation (mantissa/exponent) using e character (the output of the numbers must match up to e-6) | Decimal floating point or scientific notation (mantissa/exponent) |
| 5 | E | Scientific notation (mantissa/exponent) using E character | Decimal floating point or scientific notation (mantissa/exponent) |
| 6 | f | Decimal floating point | Decimal floating point or scientific notation (mantissa/exponent) |
| 7 | g | Uses the shortest representation of decimal floating point | Decimal floating point or scientific notation (mantissa/exponent) |
| 8 | G | Uses the shortest representation of decimal floating point | Decimal floating point or scientific notation (mantissa/exponent) |
| 9 | o | Unsigned octal | Unsigned octal |
| 10 | s | String of characters | String of characters |
| 11 | u | Unsigned decimal integer | Unsigned decimal integer |
| 12 | x | Unsigned hexadecimal integer | Unsigned hexadecimal integer (any letters) |
| 13 | X | Unsigned hexadecimal integer (capital letters) | Unsigned hexadecimal integer (any letters) |
| 14 | p | Pointer address | Pointer address |
| 15 | n | Number of characters printed until %n occurs | Number of characters scanned until %n occurs |
| 16 | % | Character % | Character % |
| No. | Flags | Description |
|---|---|---|
| 1 | - | Left-justify within the given field width; Right justification is the default (see width sub-specifier). |
| 2 | + | Forces to precede the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a -ve sign. |
| 3 | (space) | If no sign is going to be written, a blank space is inserted before the value. |
| 4 | # | Used with o, x or X specifiers the value is preceded with 0, 0x or 0X respectively for values different than zero. Used with e, E and f, it forces the written output to contain a decimal point even if no digits would follow. By default, if no digits follow, no decimal point is written. Used with g or G the result is the same as with e or E but trailing zeros are not removed. |
| 5 | 0 | Left-pads the number with zeroes (0) instead of spaces, where padding is specified (see width sub-specifier). |
| No. | Width | Description |
|---|---|---|
| 1 | (number) | Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger. |
| 2 | * | In sprintf the * sign means, that the width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted. In sscanf the * sign placed after % and before the format specifier reads data of the specified type, but suppresses their assignment. |
| No. | .precision | Description |
|---|---|---|
| 1 | .number | For integer specifiers (d, i, o, u, x, X) − precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For e, E and f specifiers − this is the number of digits to be printed after the decimal point. For g and G specifiers − This is the maximum number of significant digits to be printed. For s − this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. For c type − it has no effect. When no precision is specified for specifiers e, E, f, g and G, the default one is 6. When no precision is specified for all other kind of specifiers, the default is 1. If the period is specified without an explicit value for precision, 0 is assumed. |
| 2 | .* | The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted. |
| No. | Length | Description |
|---|---|---|
| 1 | h | The argument is interpreted as a short int or unsigned short int (only applies to integer specifiers: i, d, o, u, x and X). |
| 2 | l | The argument is interpreted as a long int or unsigned long int for integer specifiers (i, d, o, u, x and X), and as a wide character or wide character string for specifiers c and s. |
| 3 | L | The argument is interpreted as a long double (only applies to floating point specifiers − e, E, f, g and G). |
| No. | Function | Description |
|---|---|---|
| 1 | void *to_upper(const char *str) | Returns a copy of string (str) converted to uppercase. In case of any error, return NULL |
| 2 | void *to_lower(const char *str) | Returns a copy of string (str) converted to lowercase. In case of any error, return NULL |
| 3 | void *insert(const char *src, const char *str, size_t start_index) | Returns a new string in which a specified string (str) is inserted at a specified index position (start_index) in the given string (src). In case of any error, return NULL |
| 4 | void *trim(const char *src, const char *trim_chars) | Returns a new string in which all leading and trailing occurrences of a set of specified characters (trim_chars) from the given string (src) are removed. In case of any error, return NULL |
It is necessary to implement the described above functions of the string.h library:
- The library must be developed in C language of C11 standard using gcc compiler
- The library's code, including headers, makefile and library itself must be located in the src folder on the develop branch
- Do not use outdated and legacy language constructions and library functions. Pay attention to the legacy and obsolete marks in the official documentation on the language and the libraries used. Use the POSIX.1-2017 standard.
- When writing code it is necessary to follow the Google style
- Make it as a static library (with the header file s21_string.h)
- The library must be developed in accordance with the principles of structured programming, duplication in the code must be avoided
- Prepare a full coverage of the library's functions by unit-tests using the Check library
- Test's code and the executable file must be located in the src folder or its any subfolder
- Unit-tests must check the results of your implementation by comparing them with the implementation of the standard string.h library
- Unit tests must cover at least 80% of each function (checked using gcov)
- Provide a Makefile for building the library and tests (with the targets all, clean, test, s21_string.a, gcov_report)
- The gcov_report target should generate a gcov report in the form of an html page. Unit tests must be run with gcov flags to do this
- Use prefix s21_ before each function
- It is forbidden to copy the implementation of the standard string.h library and other string processing libraries and to use them anywhere, except unit-tests
- It is forbidden to use system errors arrays, including those not specified in POSIX (sys_nerr, sys_errlist). Instead, you need to implement your own platform-specific errors arrays, as it was mentioned in the description of the strerror function
- You must follow the logic of the standard string.h library (in terms of checks, working with memory and behavior in emergency situations - tests will help you with that)
- Functions must work with z-string made of single-byte characters in ASCII encoding.
It is necessary to implement the sprintf function from the stdio.h library:
- The function must be placed in the s21_string.h library
- All of the requirements outlined in the first part are applied to function implementation.
- The next partial formatting must be supported:
- Specifiers: c, d, f, s, u, %
- Flags: -, +, (space)
- Width description: (number)
- Precision description: .(number)
- Length description: h, l
Bonus assignment for extra points. It is necessary to implement some format modifiers of the sprintf function from the stdio.h library:
- The function must be placed in the s21_string.h library
- All of the requirements outlined in the first part are applied to function implementation.
- The next additional format modifiers must be supported:
- Specifiers: g, G, e, E, x, X, o, p
- Flags: #, 0
- Width description: *
- Precision description: .*
- Length description: L
Bonus assignment for extra points. It is necessary to implement the sscanf function from the stdio.h library:
- The function must be placed in the s21_string.h library
- All of the requirements outlined in the first part are applied to function implementation.
- Full formatting (including flags, widths, precision, modifiers and conversion types) must be supported.
Bonus assignment for extra points. You must implement some string processing functions from the String class (described here):
- The functions must be placed in the s21_string.h library.
- All of the requirements outlined in the first part are applied to functions implementation, excluding the requirement to compare your implementation with the standard.