C语言 如何将字符串设置为全小写
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How to set a string to all lowercase
提问by user2450044
I have a char foo[SIZE]; //(string)
我有一个 char foo[SIZE]; //(string)
and have inputed it correctly using %s(as in it printfsthe correct input), but now want to set it to lowercase. So I tried using
并使用正确输入%s（如printfs正确输入），但现在想将其设置为小写。所以我尝试使用
if (isupper(*foo))
*foo=tolower(*foo);
ie when I do:
即当我这样做时：
printf("%s" foo); //I get the same text with upper case
The text does not seem to change. Thank you.
文字似乎没有变化。谢谢你。
回答by Jerry Coffin
fooisn't a pointer, so you don't want to use it as one. You also don't have to check whether a character is an upper-case letter before using tolower-- it converts upper to lower case, and leaves other characters unchanged. You probably want something like:
foo不是指针，因此您不想将其用作指针。您也不必在使用前检查字符是否为大写字母tolower——它将大写字母转换为小写字母，而其他字符保持不变。你可能想要这样的东西：
for (i=0; foo[i]; i++)
foo[i] = tolower((unsigned char)foo[i]);
Note that when you call tolower(and toupper, isalpha, etc.) you really need to cast your input to unsigned char. Otherwise, many (most?) characters outside the basic English/ASCII character set will frequently lead to undefined behavior (e.g., in a typical case, most accented characters will show up as negative numbers).
请注意，当您调用tolower（和toupper、isalpha等）时，您确实需要将输入转换为unsigned char. 否则，基本英语/ASCII 字符集之外的许多（大多数？）字符将经常导致未定义的行为（例如，在典型情况下，大多数重音字符将显示为负数）。
As an aside, when you're reading the string, you don't want to use scanfwith %s-- you always want to specify the string length, something like: scanf("%19s", foo);, assuming SIZE== 20 (i.e., you want to specify one less than the size. Alternatively, you could use fgets, like fgets(foo, 20, infile);. Note that with fgets, you specify the size of the buffer, not one less like you do with scanf(and company like fscanf).
顺便说一句，当您读取字符串时，您不想使用scanfwith %s-- 您总是想指定字符串长度，例如: scanf("%19s", foo);，假设SIZE== 20（即，您想指定一个小于大小。或者，您可以使用fgets，例如fgets(foo, 20, infile);。请注意，使用fgets，您指定缓冲区的大小，而不是像您使用的那样scanf（以及像 fscanf这样的公司）。
回答by Bill
Try this
尝试这个
for(i = 0; foo[i]; i++){
foo[i] = tolower(foo[i]);
}
回答by Grzegorz Piwowarek
*foo=tolower(*foo); //doing *(foo+i) or foo[i] does not work either
*foo=tolower(*foo); //doing *(foo+i) or foo[i] does not work either
because all of those options do not make sense
因为所有这些选项都没有意义
You should use it like this:
你应该像这样使用它：
for(i = 0; foo[i] != '##代码##'; i++){
foo[i] = tolower(foo[i]);
}
