Standard Library

C Standard Library

The C standard library operates on character arrays char[]/const char*.

See: fprintf, fscanf, null-terminated byte strings

• printf("%s", s): use %s to output a string (character array).
• scanf("%s", &s): use %s to read a string (character array).
• sscanf(const char *__source, const char *__format, ...): read variables from the string __source, for example, sscanf(str,"%d",&a).
• sprintf(char *__stream, const char *__format, ...): output the contents of the __format string to __stream, for example, sprintf(str,"%d",i).
• strlen(const char *str): return the number of characters from str[0] up to '\0'. Note that without O2 optimization, placing this operation in a loop condition has complexity $\Theta(N)$.
• strcmp(const char *str1, const char *str2): compare str1 str2 lexicographically. Return a negative value if str1 is lexicographically smaller, 0 if they are equal, and a positive value if str1 is lexicographically larger. Note that the return value is not necessarily one of only 0, 1, and -1; on different platforms, it follows the sign convention but need not be exactly 0, 1, or -1.
• strcpy(char *str, const char *src): copy the characters in src to str. Both str and src are pointers to the first element of character arrays. The return value is str, including the null terminator '\0'.
• strncpy(char *str, const char *src, int cnt): copy at most cnt characters to str. If src ends before cnt characters have been copied, write null characters to str until a total of cnt characters have been written.
• strcat(char *str1, const char *str2): append str2 to the end of str1, replacing the final '\0' of str1 with *str2, and return str1.
• strstr(char *str1, const char *str2): if str2 is a substring of str1, return the address of its first occurrence in str1; if str2 is not a substring of str1, then str2 is not present and the function returns NULL.
• strchr(const char *str, int c): find the first occurrence of character c in string str and return its address. If the character is not found, return NULL.
• strrchr(const char *str, int c): find the last occurrence of character c in string str and return its address. If the character is not found, return NULL.

C++ Standard Library

The C++ standard library operates on string objects std::string, while also providing compatibility with character arrays.

See: std::basic_string, std::basic_string_view

• The overloaded assignment operator + can concatenate two variables when + is on both sides and the operands have types string/char/char[]/const char*, returning the concatenated string (string).
• The right-hand side of the assignment operator = can be const string/string/const char*/char*.
• The access operator [cur] returns a reference to position cur.
• The access functions data()/c_str() return a const char* pointer whose contents are the same as the string.
• The capacity function size() returns the number of characters in the string.
• find(ch, start = 0) searches for and returns the position of character ch starting from start; rfind(ch) searches backward from the end and returns the position of the first found character ch (both positions start at 0). If the character is not found, return -1.
• substr(start, len) extracts a string of length len from start (starting at 0) in the string (if len is omitted, extract to the end of the string).
• append(s) adds s to the end of the string.
• append(s, pos, n) appends the n characters of string s starting at pos to the end of the current string.
• replace(pos, n, s) deletes n characters starting at pos, then inserts string s at pos.
• erase(pos, n) deletes n characters starting at pos.
• insert(pos, s) inserts string s at position pos.
• std::string overloads the comparison and logical operators; their complexity is $\Theta(N)$.