• atoi() & itoa()函数的内部的实现


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    1. /***
    2. *atox.c - atoi and atol conversion
    3. *
    4. * Copyright (c) 1989-1997, Microsoft Corporation. All rights reserved.
    5. *
    6. *Purpose:
    7. * Converts a character string into an int or long.
    8. *
    9. *******************************************************************************/

    11. #include <cruntime.h>
    12. #include <stdlib.h>
    13. #include <ctype.h>

    15. /***
    16. *long atol(char *nptr) - Convert string to long
    17. *
    18. *Purpose:
    19. * Converts ASCII string pointed to by nptr to binary.
    20. * Overflow is not detected.
    21. *
    22. *Entry:
    23. * nptr = ptr to string to convert
    24. *
    25. *Exit:
    26. * return long int value of the string
    27. *
    28. *Exceptions:
    29. * None - overflow is not detected.
    30. *
    31. *******************************************************************************/

    33. long __cdecl atol(
    34. const char *nptr
    35. )
    36. {
    37. int c; /* current char */
    38. long total; /* current total */
    39. int sign; /* if ''-'', then negative, otherwise positive */

    41. /* skip whitespace */
    42. while ( isspace((int)(unsigned char)*nptr) )
    43. ++nptr;

    45. c = (int)(unsigned char)*nptr++;
    46. sign = c; /* save sign indication */
    47. if (c == ''-'' || c == ''+'')
    48. c = (int)(unsigned char)*nptr++; /* skip sign */

    50. total = 0;

    52. while (isdigit(c)) {
    53. total = 10 * total + (c - ''0''); /* accumulate digit */
    54. c = (int)(unsigned char)*nptr++; /* get next char */
    55. }

    57. if (sign == ''-'')
    58. return -total;
    59. else
    60. return total; /* return result, negated if necessary */
    61. }


    64. /***
    65. *int atoi(char *nptr) - Convert string to long
    66. *
    67. *Purpose:
    68. * Converts ASCII string pointed to by nptr to binary.
    69. * Overflow is not detected. Because of this, we can just use
    70. * atol().
    71. *
    72. *Entry:
    73. * nptr = ptr to string to convert
    74. *
    75. *Exit:
    76. * return int value of the string
    77. *
    78. *Exceptions:
    79. * None - overflow is not detected.
    80. *
    81. *******************************************************************************/

    83. int __cdecl atoi(
    84. const char *nptr
    85. )
    86. {
    87. return (int)atol(nptr);
    88. }

    90. #ifndef _NO_INT64

    92. __int64 __cdecl _atoi64(
    93. const char *nptr
    94. )
    95. {
    96. int c; /* current char */
    97. __int64 total; /* current total */
    98. int sign; /* if ''-'', then negative, otherwise positive */

    100. /* skip whitespace */
    101. while ( isspace((int)(unsigned char)*nptr) )
    102. ++nptr;

    104. c = (int)(unsigned char)*nptr++;
    105. sign = c; /* save sign indication */
    106. if (c == ''-'' || c == ''+'')
    107. c = (int)(unsigned char)*nptr++; /* skip sign */

    109. total = 0;

    111. while (isdigit(c)) {
    112. total = 10 * total + (c - ''0''); /* accumulate digit */
    113. c = (int)(unsigned char)*nptr++; /* get next char */
    114. }

    116. if (sign == ''-'')
    117. return -total;
    118. else
    119. return total; /* return result, negated if necessary */
    120. }

    122. #endif /* _NO_INT64 */


    125. #include <msvcrt/errno.h>
    126. #include <msvcrt/stdlib.h>
    127. #include <msvcrt/internal/file.h>
    128. char* _itoa(int value, char* string, int radix)
    129. {
    130. char tmp[33];
    131. char* tp = tmp;
    132. int i;
    133. unsigned v;
    134. int sign;
    135. char* sp;

    137. if (radix > 36 || radix <= 1)
    138. {
    139. __set_errno(EDOM);
    140. return 0;
    141. }

    143. sign = (radix == 10 && value < 0);
    144. if (sign)
    145. v = -value;
    146. else
    147. v = (unsigned)value;
    148. while (v || tp == tmp)
    149. {
    150. i = v % radix;
    151. v = v / radix;
    152. if (i < 10)
    153. *tp++ = i+''0'';
    154. else
    155. *tp++ = i + ''a'' - 10;
    156. }

    158. if (string == 0)
    159. string = (char*)malloc((tp-tmp)+sign+1);
    160. sp = string;

    162. if (sign)
    163. *sp++ = ''-'';
    164. while (tp > tmp)
    165. *sp++ = *--tp;
    166. *sp = 0;
    167. return string;
    168. }

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  • 原文地址：https://www.cnblogs.com/black/p/5171831.html
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