字符串或字符到整数问题 [英] string or character to integer problem
问题描述
有人能告诉我下面的代码片段有什么问题吗？
char a = x [index];
char b = y [index ];
int result = strtol（& a，NULL，10）+ strtol（& b，NULL，10）;
我得到了结果使用result = atoi（& a）+ atoi（& b）;
cout<< a<< ''\t''<< b<< ENDL;显示a和b的值是正确的。
cout<< atoi（& a）（或strtol（& a，NULL，10））是正确的但是atoi（& b）和
strtol（& b，NULL，10）是不正确的。
这个项目假设采用无限制的整数。大小并添加它们。
Mandrake Linux 10，gcc-c ++ - 3.3.2-6mdk，内核2.6.3-15mdk
Can anyone tell me what is wrong with the following code fragment?
char a = x[index];
char b = y[index];
int result = strtol(&a, NULL, 10) + strtol(&b, NULL, 10);
I got the same result using result=atoi(&a)+atoi(&b);
cout << a << ''\t'' << b << endl; shows the values of a and b to be correct.
cout << atoi(&a) (or strtol(&a, NULL, 10)) is correct but atoi(&b) and
strtol(&b, NULL, 10) are incorrect.
This project is suppose to take integers of "unlimited" size and add them.
Mandrake Linux 10, gcc-c++-3.3.2-6mdk, kernel 2.6.3-15mdk
推荐答案
2004年7月17日星期六23:30:07 GMT in comp.lang.c ++， jo **** @ n0sq.net
写道，
On Sat, 17 Jul 2004 23:30:07 GMT in comp.lang.c++, jo****@n0sq.net
wrote,
有谁能告诉我下面的代码片段有什么问题？
char a = x [index];
char b = y [index];
int result = strtol（& a，NULL，10）+ strtol（& b，NULL，10）;
Can anyone tell me what is wrong with the following code fragment?
char a = x[index];
char b = y[index];
int result = strtol(&a, NULL, 10) + strtol(&b, NULL, 10);
strtol没有指向单个char的指针。很少有事情可做;
当你看到（char *）你通常可以认为它是一个指向
字符数组的指针，并且通常是零终止的字符串。
无论如何使用strtol转换单个字符串都是愚蠢的，只需减去
''\ 0''。
strtol does not take a pointer to a single char. Very few things do;
when you see (char *) you can usually assume that it is a pointer to an
array of chars, and most often a zero-terminated string.
Using strtol to convert a single char is silly anyway, just subtract
''\0''.
David Harmon写道：
David Harmon wrote:
2004年7月17日星期六23:30:07 GMT in comp.lang.c ++， jo **** @ n0sq.net
写道，
On Sat, 17 Jul 2004 23:30:07 GMT in comp.lang.c++, jo****@n0sq.net
wrote,
谁能告诉我有什么问题？以下代码片段？
char a = x [index];
char b = y [index];
int result = strtol（& a，NULL，10） + strtol（& b，NULL，10）;
Can anyone tell me what is wrong with the following code fragment?
char a = x[index];
char b = y[index];
int result = strtol(&a, NULL, 10) + strtol(&b, NULL, 10);
strtol不会指向单个char。很少有事情可做;
当你看到（char *）时，你通常会认为它是指向一组字符的指针，通常是一个以零结尾的字符串。
strtol does not take a pointer to a single char. Very few things do;
when you see (char *) you can usually assume that it is a pointer to an
array of chars, and most often a zero-terminated string.
Using strtol to convert a single char is silly anyway, just subtract
''\0''.
我不确定关于减法你想说什么。
无论如何，我通常使用atoi（）将一个字符（或字符串）转换为
整数。可能有更好的方法来做我想做的事情但是这个
无论如何都是初稿。我需要能够添加2个大于/或
的大整数，而不是存储在无符号长整数中。
事实证明，在我的系统上，任何整数类型使用4个字节（根据
从sizeof（）返回）。无论如何，我正在输入值作为字符串和
将它们存储在一个向量中。
此外，我仍然需要知道为什么第一次调用strtol（）返回
正确值，而第二次调用strtol（）则没有。
I''m not sure of what you''re trying to say about the subtraction.
Anyway, I normally use atoi() to convert a character (or string) to an
integer. There''s probably a better way to do what I''m trying to do but this
is a first draft anyway. I need to be able to add 2 large integers that are
larger than can be stored in an unsigned long.
As it turns out, on my system, any integer type uses 4 bytes (according to
the return from sizeof()). Anyway, I''m entering the values as strings and
storing them in a vector.
Besides, I still need to know why the first call to strtol() returns the
correct value while the second call to strtol() doesn''t.
在Sun上， 2004年7月18日01:58:27 GMT在comp.lang.c ++中， jo****@n0sq.net
写道，
On Sun, 18 Jul 2004 01:58:27 GMT in comp.lang.c++, jo****@n0sq.net
wrote,
我不确定你想要减法的内容。
无论如何我在那部分犯了一个错误。我的意思是，如果a在''0'到''9''范围内是$
，则a - ''0''是
$中的对应值b $ b范围是0到9.
无论如何，我通常使用atoi（）将字符（或字符串）转换为
整数。
再次，atoi（），strtol（）等仅用于转换零终止的c / /
样式数组字符串，从不单个字符。如果它适用于单个
char变量，那只是好运或坏运气。
此外，我仍然需要知道为什么第一次调用strtol（）会返回<第二次调用strtol（）时没有正确的值。
I''m not sure of what you''re trying to say about the subtraction.
I made a mistake in that part anyway. What I mean is that if a is char
in the range ''0'' through ''9'', then a-''0'' is the corresponding value in
the range 0 through 9.
Anyway, I normally use atoi() to convert a character (or string) to an
integer.
Again, atoi(), strtol(), etc are only for converting zero-terminated c
style array strings, never single characters. If it works for single
char variables it is only by good or bad luck.
Besides, I still need to know why the first call to strtol() returns the
correct value while the second call to strtol() doesn''t.
这取决于偶然发生在内存中跟踪变量的情况。 />
第一个和第二个仍然同样错误。
It depends on what happens by chance to follow the variable in memory.
Both the first and thee second are still equally wrong.
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