C ++ type conversion atoi atol atof, ITOA ftoa char string

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1. atoi

int atoi ( const char * str );

Convert string to integer

Parses the C stringStrInterpreting its content as an integral number, which is returned as
IntValue.

/* atoi example */#include <stdio.h>#include <stdlib.h>int main (){  int i;  char szInput [256];  printf ("Enter a number: ");  fgets ( szInput, 256, stdin );  i = atoi (szInput);  printf ("The value entered is %d. The double is %d.\n",i,i*2);  return 0;}

Output

Enter a number: 73The value entered is 73. The double is 146.

2. atol

long int atol ( const char * str );

Convert string to long integer

Parses the C stringStrInterpreting its content as an integral number, which is returned as
Long intValue.

/* atol example */#include <stdio.h>#include <stdlib.h>int main (){  long int li;  char szInput [256];  printf ("Enter a long number: ");  gets ( szInput );  li = atol (szInput);  printf ("The value entered is %d. The double is %d.\n",li,li*2);  return 0;}

Output

Enter a number: 567283The value entered is 567283. The double is 1134566.

3. atof

double atof ( const char * str );

Convert string to double

Parses the C stringStrInterpreting its content as a floating point number and returns its value as
Double.

/* atof example: sine calculator */#include <stdio.h>#include <stdlib.h>#include <math.h>int main (){  double n,m;  double pi=3.1415926535;  char szInput [256];  printf ( "Enter degrees: " );  gets ( szInput );  n = atof ( szInput );  m = sin (n*pi/180);  printf ( "The sine of %f degrees is %f\n" , n, m );  return 0;}OutputEnter degrees: 45The sine of 45.000000 degrees is 0.707101

4. ITOA

char *  itoa ( int value, char * str, int base );

Convert integer to string (non-standard function)

Converts an integerValueTo a null-terminated string using the specified
BaseAnd stores the result in the array givenStrParameter.

This function is not defined in ANSI-C and is not part of C++, but is supported by some compilers.A standard-compliant alternative for some cases may be sprintf:

• Sprintf (STR, "% d", value) converts to decimal base.
• Sprintf (STR, "% x", value) converts to hexadecimal base.
• Sprintf (STR, "% O", value) converts to octal Base

/* itoa example */#include <stdio.h>#include <stdlib.h>int main (){  int i;  char buffer [33];  printf ("Enter a number: ");  scanf ("%d",&i);  itoa (i,buffer,10);  printf ("decimal: %s\n",buffer);  itoa (i,buffer,16);  printf ("hexadecimal: %s\n",buffer);  itoa (i,buffer,2);  printf ("binary: %s\n",buffer); return 0;}

Output

Enter a number: 1750decimal: 1750hexadecimal: 6d6binary: 11011010110

5. ftoa

#include <sstream>string convertDouble(double value) {  std::ostringstream o;  if (!(o << value))    return "";  return o.str();}

6. string to Char

1. the const char * c_str (); c_str () function returns a pointer to a regular C string with the same content as the string. this is to be compatible with the C language and has no string type in the C language. Therefore, you must use the member function c_str () of the string class object to convert the string object to the string style in C. Note: You must use strcpy () and other functions to operate the pointer returned by c_str (). For example, it is best not to use the following code: char * C; string S = "1234"; C = S. c_str (); // The final content pointed to by C is garbage. Because the S object is destructed, the content should be processed as follows: Char C [20]; string S = "1234"; strcpy (C, S. c_str (); in this way, no error occurs. c_str () returns a temporary pointer and cannot operate on it (only copy it () returns the string containing a string in the form of char *. If a function requires the char * parameter, you can use the c_str () method: String S = "Hello world! "; Printf (" % s ", S. c_str (); // output" Hello world! "2. Const * char c_str () a function that converts string to const * char. The pointer returned by string c_str () is managed by string. Its life cycle is the life cycle of the string object. Then you can use this pointer in the form of C or copy its content. Example: String s; CIN> S; const char * Ch = S. c_str (); in this way, you can input any long string from the standard input and use it according to const * char. 3. to convert a char to a string, you can use string S (char *); 4. other conversion methods: Convert string to cstring. format ("% s", String. c_str (); Char to cstring. format ("% s", char *); notes:

[Conversion] C ++ int, Char, String, cstring type conversion (Summary)

# Include <string>// When using the string class of the C ++ standard library

Using namespace STD;// Same as above

# Include <sstream>

# Include <iostream>

# Include <stdlib. h>// It is best to directly convert the string and INT types to include,

// Because it is easier to write a conversion function by yourself, the function definition is as follows:

String getstring (const int N)

{

STD: stringstream newstr;
Newstr <N;
Return newstr. STR ();

}

String to cstring
Cstring. Format ("% s", String. c_str ());

Convert Char to cstring
Cstring. Format ("% s", char *);

Char to string
String S (char *);

String to char *
Char * P = string. c_str ();

Cstring to string
String S (cstring. getbuffer ());

1, string-> cstring
Cstring. Format ("% s", String. c_str ());
C_str () is indeed better than data.
2, char-> string
String S (char *);
Only Initialization is allowed. It is best to use assign () instead of initialization ().
3, cstring-> string
String S (cstring. getbuffer ());
Releasebuffer () is required after getbuffer (). Otherwise, no space occupied by the buffer is released.

As mentioned in C ++ standard function library
There are three functions that can convert the content of a string to a character array and a C-string
1. Data (), returns a string array without "\ 0"
2, c_str (), returns a string array with "\ 0"
3, copy ()

---------------------

Conversion between cstring, Int, char *, and char [100 --

Conversion between cstring, Int, char *, and char [100 --

Cstring mutual int Conversion

Converts a character to an integer. You can use atoi, _ atoi64, or atol.
To convert a number to a cstring variable, you can use the format function of cstring. For example
Cstring S;
Int I = 64;
S. Format ("% d", I)
The format function is very powerful and worth your research.

Void cstrdlg: onbutton1 ()
{
// Todo: add your control notification handler code here
Cstring
Ss = "1212.12 ″;
Int temp = atoi (SS );
Cstring AA;
AA. Format ("% d", temp );
Afxmessagebox ("VaR is" + AA );
}

Sart. Format ("% s", Buf );

Convert cstring to char *

/// Char * To cstring
Cstring strtest;
Char * charpoint;
Charpoint = "give string a value ";
Strtest = charpoint;

/// Cstring to char *
Charpoint = strtest. getbuffer (strtest. getlength ());

There is no string in Standard C, char * = char [] = string

You can use the cstring. Format ("% s", char *) method to convert char * To cstring. To convert cstring to char *, use the operator (lpcstr) cstring.

Cstring conversion char [100]

Char A [100];
Cstring STR ("aaaaaa ");
Strncpy (A, (lpctstr) STR, sizeof ());