itoa()和atoi()/atol()的源码

1. /***
2. *atox.c-atoiandatolconversion
3. *
4. *Copyright(c)1989-1997,MicrosoftCorporation.Allrightsreserved.
5. *
6. *Purpose:
7. *Convertsacharacterstringintoanintorlong.
8. *
9. *******************************************************************************/
11. #include<cruntime.h>
12. #include<stdlib.h>
13. #include<ctype.h>
15. /***
16. *longatol(char*nptr)-Convertstringtolong
17. *
18. *Purpose:
19. *ConvertsASCIIstringpointedtobynptrtobinary.
20. *Overflowisnotdetected.
21. *
22. *Entry:
23. *nptr=ptrtostringtoconvert
24. *
25. *Exit:
26. *returnlongintvalueofthestring
27. *
28. *Exceptions:
29. *None-overflowisnotdetected.
30. *
31. *******************************************************************************/
33. long__cdeclatol(
34. constchar*nptr
35. )
36. {
37. intc;/*currentchar*/
38. longtotal;/*currenttotal*/
39. intsign;/*if''-'',thennegative,otherwisepositive*/
41. /*skipwhitespace*/
42. while(isspace((int)(unsignedchar)*nptr))
43. ++nptr;
45. c=(int)(unsignedchar)*nptr++;
46. sign=c;/*savesignindication*/
47. if(c==''-''||c==''+'')
48. c=(int)(unsignedchar)*nptr++;/*skipsign*/
50. total=0;
52. while(isdigit(c)){
53. total=10*total+(c-''0'');/*accumulatedigit*/
54. c=(int)(unsignedchar)*nptr++;/*getnextchar*/
55. }
57. if(sign==''-'')
58. return-total;
59. else
60. returntotal;/*returnresult,negatedifnecessary*/
61. }
64. /***
65. *intatoi(char*nptr)-Convertstringtolong
66. *
67. *Purpose:
68. *ConvertsASCIIstringpointedtobynptrtobinary.
69. *Overflowisnotdetected.Becauseofthis,wecanjustuse
70. *atol().
71. *
72. *Entry:
73. *nptr=ptrtostringtoconvert
74. *
75. *Exit:
76. *returnintvalueofthestring
77. *
78. *Exceptions:
79. *None-overflowisnotdetected.
80. *
81. *******************************************************************************/
83. int__cdeclatoi(
84. constchar*nptr
85. )
86. {
87. return(int)atol(nptr);
88. }
90. #ifndef_NO_INT64
92. __int64__cdecl_atoi64(
93. constchar*nptr
94. )
95. {
96. intc;/*currentchar*/
97. __int64total;/*currenttotal*/
98. intsign;/*if''-'',thennegative,otherwisepositive*/
100. /*skipwhitespace*/
101. while(isspace((int)(unsignedchar)*nptr))
102. ++nptr;
104. c=(int)(unsignedchar)*nptr++;
105. sign=c;/*savesignindication*/
106. if(c==''-''||c==''+'')
107. c=(int)(unsignedchar)*nptr++;/*skipsign*/
109. total=0;
111. while(isdigit(c)){
112. total=10*total+(c-''0'');/*accumulatedigit*/
113. c=(int)(unsignedchar)*nptr++;/*getnextchar*/
114. }
116. if(sign==''-'')
117. return-total;
118. else
119. returntotal;/*returnresult,negatedifnecessary*/
120. }
122. #endif/*_NO_INT64*/
125. #include<msvcrt/errno.h>
126. #include<msvcrt/stdlib.h>
127. #include<msvcrt/internal/file.h>
128. char*_itoa(intvalue,char*string,intradix)
129. {
130. chartmp[33];
131. char*tp=tmp;
132. inti;
133. unsignedv;
134. intsign;
135. char*sp;
137. if(radix>36||radix<=1)
138. {
139. __set_errno(EDOM);
140. return0;
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. returnstring;
168. }
170. PS1:atoi()可以用二维数组的索引来实现，避免*10的循环。
172. PS2:itoa()采用返回堆指针的方式得到结果，不会造成memoryleak和指针问题。但是不可以通过传入的char*string返回结果，会造成指针问题。（可以改写为char**string，因此微软的sdk中实现的方式有问题）
173. 注：源码可在VC目录下找到