C++ 将字符串中的字符与给定的字符进行比较
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Compare between a char in a string to a given char
提问by Itzik984
I have the following:
我有以下几点：
int findPar(char* str)
{
int counter=0;
while (*str)
{
if(str[0] == "(") <---- Warning
{
counter++;
}
else if (str[0]== ")") <---- Warning
{
counter--;
}
if (counter<0)
{
return 0;
}
str++;
}
if (counter!=0)
{
return 0;
}
return 1;
}
The warning i get is comparison between an int and a char.
我得到的警告是 int 和 char 之间的比较。
I tried to do the comparison (first char in the string vs. given char) also with strcmp like this:
我也尝试使用 strcmp 进行比较（字符串中的第一个字符与给定的字符），如下所示：
if (strcmp(str, ")")==0) { stuff }
but it never goes in to 'stuff' even when the comparison (should) be correct.
但即使比较（应该）是正确的，它也永远不会进入“东西”。
how should i do it?
我该怎么做？
回答by Imp
If stris a C string (null-terminated array of chars), then str[0]is a char.
如果str是 C 字符串（以空字符结尾的字符数组），则str[0]是一个字符。
Note that the type of quotes matters! ')'is a char, while ")"is a string (i.e. a ')'char followed by a null terminator).
请注意，引号的类型很重要！')'是一个字符，")"而是一个字符串（即一个')'字符后跟一个空终止符）。
So, you may compare two chars:
因此，您可以比较两个字符：
str[0] == ')'
or you may compare two strings
或者你可以比较两个字符串
strcmp(str, ")") == 0
naturally, (the second works if strstring really only contains that parenthesis).
自然，（如果str字符串真的只包含该括号，则第二个有效）。
回答by Seth Carnegie
You're comparing a character (str[0]) with a const char[N]("whatever"). You need to use single quotes because double quotes denote character arrays, whereas single quotes denote single characters:
您正在将字符 ( str[0]) 与const char[N]( "whatever")进行比较。您需要使用单引号，因为双引号表示字符数组，而单引号表示单个字符：
if (str[0] == ')') // or *str == ')'
Etc.
等等。
The reason why strcmpwas failing as well was because, while the string at some time does point to the ), it has more characters beyond that (i.e. is not followed immediately by a '\0') so the string is not equivalent to the string ")"which has one character.
strcmp失败的原因也是因为，虽然字符串在某些时候确实指向)，但它还有更多的字符（即后面没有紧跟 a '\0'），因此该字符串不等同于")"具有一个字符的字符串。
回答by Daniel Fischer
Double quotes, "are string delimiters, so ")"is a pointer to a string literal in if(str[0] == "(").
You want to compare to a character, so you have to use single quotes
双引号"是字符串分隔符，因此")"是if(str[0] == "("). 你想与一个字符进行比较，所以你必须使用单引号
if(str[0] == '(')
回答by Kerrek SB
You need if (str[0] == ')')etc. Note the single quotation marks (apostrophes) to denote character literals.
您需要if (str[0] == ')')等。请注意单引号（撇号）表示字符文字。
