atoi、atof、itoa、itow函數(shù)是windows平臺下實(shí)現(xiàn)字符串與數(shù)值相互轉(zhuǎn)換的函數(shù)。Linux平臺下請使用標(biāo)準(zhǔn)庫中的sprintf與sscanf函數(shù)。

atoi函數(shù)

原型：int atoi( const char *string );

ASCII to integer

作用：將字符串轉(zhuǎn)為integer類型

atof函數(shù)

原型：double atof( const char *string );

ASCII to float

作用：將字符串轉(zhuǎn)為double類型

對于以上函數(shù)，若字符串無法轉(zhuǎn)化為合法的數(shù)值類型，函數(shù)將返回0 。

Code
1#include <stdlib.h>
2#include <stdio.h>
3
4void main( void )
5{
6   char *s; double x; int i; long l;
7
8    printf( " testing atoi,atof,atol function :\n" ) ;
9    s = "   -2309.12E-15";    /**//* Test of atof */
10    x = atof( s );
11    printf( "atof test: ASCII string: %s\tfloat:   %e\n", s, x );
12
13    s = "7.8912654773d210";  /**//* Test of atof */
14    x = atof( s );
15    printf( "atof test: ASCII string: %s\tfloat:   %e\n", s, x );
16
17    s = "   -9885 pigs";      /**//* Test of atoi */
18    i = atoi( s );
19    printf( "atoi test: ASCII string: %s\t\tinteger: %d\n", s, i );
20
21    s = "98854 dollars";     /**//* Test of atol */
22    l = atol( s );
23    printf( "atol test: ASCII string: %s\t\tlong: %ld\n", s, l );
24}
25

atof test: ASCII string:   -2309.12E-15 float: -2.309120e-012

atof test: ASCII string: 7.8912654773d210 float: 7.891265e+210

atoi test: ASCII string:   -9885 pigs    integer: -9885

atol test: ASCII string: 98854 dollars    long: 98854

_itoa函數(shù)

原型：char *_itoa( int value, char *str, int radix );//2<=radix<=36

Integer to ASCII

作用：將Integer類型轉(zhuǎn)換為radix進(jìn)制，然后以ASCII字符串的形式存放在str中

_itow函數(shù)

wchar_t * _itow( int value, wchar_t *str, int radix ); //2<=radix<=36

Integer to Wide Char

作用：將Integer類型轉(zhuǎn)換為radix進(jìn)制，然后以寬字符串的形式存放在str中

    以上2個(gè)函數(shù)均有安全隱患（當(dāng)字符數(shù)組長度不足保存結(jié)果時(shí)會導(dǎo)致緩沖區(qū)溢出），在vs2008中編譯時(shí)會有警告。推薦使用它們的安全版本—— _itoa_s與_itow_s 。

_itoa_s 函數(shù)原型如下：

errno_t _itoa_s(

   int value,

   char *buffer,

   size_t sizeInCharacters, //存放結(jié)果的字符數(shù)組長度

   int radix

);

當(dāng)轉(zhuǎn)換的結(jié)果長度比sizeInCharacters變量大時(shí)，由于出現(xiàn)access violation，函數(shù)將馬上終止，而_itoa函數(shù)將繼續(xù)運(yùn)行。

使用范例（來自MSDN）：

Code
1#include<string.h>
2#include<stdlib.h>
3#include<stdio.h>
4
5int main( void )
6{
7   char buffer[65];
8   int r;
9    printf( "test _itoa function ! \n" ) ;
10   for( r=10; r>=2; --r )
11   {
12      _itoa( -1, buffer, r ); // C4996
13     // Note: _itoa is deprecated; consider using _itoa_s instead
14      printf( "base %d: %s (%d chars)\n", r, buffer, strnlen(buffer, _countof(buffer)) );
15    }
16
17    printf( "test _itoa_s function ! \n " ) ;
18   for( r=10; r>=2; --r )
19   {
20       _itoa_s( -1, buffer, 65, r );
21       printf( "base %d: %s (%d chars)\n", r, buffer, strnlen(buffer, _countof(buffer)) );
22    }
23}
24

輸出：

base 10: -1 (2 chars)

base 9: 12068657453 (11 chars)

base 8: 37777777777 (11 chars)

base 7: 211301422353 (12 chars)

base 6: 1550104015503 (13 chars)

base 5: 32244002423140 (14 chars)

base 4: 3333333333333333 (16 chars)

base 3: 102002022201221111210 (21 chars)

base 2: 11111111111111111111111111111111 (32 chars)

base 10: -1 (2 chars)

base 9: 12068657453 (11 chars)

base 8: 37777777777 (11 chars)

base 7: 211301422353 (12 chars)

base 6: 1550104015503 (13 chars)

base 5: 32244002423140 (14 chars)

base 4: 3333333333333333 (16 chars)

base 3: 102002022201221111210 (21 chars)

base 2: 11111111111111111111111111111111 (32 chars)