The prototypes for the some common functions in the C++ standard library are listed below.  These prototypes and the functions definitions are declared within the std namespace.  To access one of these functions, we #include its parent header file and either expose the entire namespace (using namespace std;) or add the std:: prefix to the function identifier.

C Library

<cstdio> - Standard and File Input Output

• int scanf(const char* format, ...) - read data from standard input
  
• int printf(const char* format, ...) - send data to standard output
  
• int fscanf(FILE* stream, const char* format, ...) - read data from a file stream
  
• int fprintf(FILE* stream, const char* format, ...) - send data to a file stream
  

<cstring> - C-Style Null-Terminated Strings

• size_t - non-negative integer type
  
• size_t strlen(const char* str) - the number of characters in a C-style null-terminated string
  
• char* strcpy(char* destination, const char* source) - copy C-style null-terminated string from source address to destination address
  
• char* strcat(char* destination, const char* source) - concatenate C-style null-terminated string from source address to the string at the destination address
  
• int strcmp(const char* str1, const char* str2) - compare C-style null-terminated strings at two addresses
  

<cstdlib> - General Utilities

• int abs(int i) - absolute value of i
  
• int atoi(const char* str) - convert C-style null-terminated string (str) to an integer
  
• int rand() - generate a random number
  

<cmath> - Numerics

• double abs(double x) - absolute value of x
  
• float abs(float x) - absolute value of x
  
• double pow(double base, double exponent) - raises base to the power of exponent
  
• double sqrt(double x) - square root of x
  

<cctype> - Character Handling

• int toupper(int c) - converts c to upper case
  
• int tolower(int c) - converts c to lower case
  
• int isupper(int c) - is c upper case?
  
• int islower(int c) - is c lower case?
  
• int isalpha(int c) - is c alphabetic?
  
• int isdigit(int c) - is c a numeric digit?
  

Input Output Library

<iostream> - Standard Input Output Objects

• streamsize - integer type
  
• fmtflags - format flags type
  
• char fill(char c) - set fill character to c
  
• fmtflags setf(fmtflags f) - set format to f
  
• fmtflags unsetf(fmtflags f) - unset format for f
  
• streamsize width(streamsize w) - set field width to w
  
• streamsize precision(streamsize p) - set floating-point precision to p
  
• bool good() const - goo bit is set
  
• bool eof() const - end of file bit is set
  
• bool fail() const - fail file bit is set
  
• bool bad() const - bad bit is set
  
• bool eof() const - end of file bit is set
  
• void clear() - set error state to good
  

<iomanip> - Parametric Manipulators

• setfill(char c) - set fill character to c
  
• setw(int w) - set field width to w
  
• setprecision(int p) - set floating-point precision to p
  

<fstream> - File Input Output Objects

• void open(const char* f, ...) - open file named f and associate it with the current object
  
• void close() - close file associated with current object