C语言 如何使用 printf 打印非空终止字符串？
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How do I print a non-null-terminated string using printf?
提问by Mike
How can I print a non-null-terminated string using printf, assuming that I know the length of the string at runtime?
假设我在运行时知道字符串的长度，如何使用 printf 打印非空终止字符串？
回答by kennytm
printf("%.*s", length, string);
Use together with other args:
与其他参数一起使用：
printf("integer=%d, string=%.*s, number=%f", integer, length, string, number);
// ^^^^ ^^^^^^^^^^^^^^
In C you could specify the maximum length to output with the %.123sformat. This means the output length is at most 123 chars. The 123could be replaced by *, so that the length will be taken from the argument of printf instead of hard-coded.
在 C 中，您可以指定%.123s格式输出的最大长度。这意味着输出长度最多为 123 个字符。所述123可以被替代*，从而使长度将从printf的的参数，而不是硬编码要采取。
Note that this assumes the stringdoes not contain any interior null bytes (\0), as %.123sonly constrains the maximumlength not the exactlength, and strings are still treated as null-terminated.
请注意，这假定string不包含任何内部空字节 (\0)，因为%.123s仅限制最大长度而不是确切长度，并且字符串仍被视为以空字符结尾。
If you want to print a non-null-terminated string with interior null, you cannot use a single printf. Use fwriteinstead:
如果要打印内部为空的非空终止字符串，则不能使用单个 printf。使用fwrite来代替：
fwrite(string, 1, length, stdout);
See @M.S.Dousti's answerfor detailed explanation.
有关详细说明，请参阅@MSDousti 的回答。
回答by M.S. Dousti
The answer provided by @KennyTM is great, but with a subtlety.
@KennyTM 提供的答案很棒，但也很微妙。
In general, if the string is non-null "terminated", but has a null character in the middle, printf("%.*s", length, string);does not work as expected. This is because the %.*sformat string asks printfto print a maximumof lengthcharacters, not exactlylengthcharacters.
一般来说，如果字符串是非空的“终止”，但中间有一个空字符，printf("%.*s", length, string);则不会按预期工作。这是因为%.*s格式字符串要求printf打印最大的length人物，不准确length的字符。
I'd rather use the more general solution pointed out by @William Pursell in a comment under the OP:
我宁愿使用@William Pursell 在 OP 下的评论中指出的更通用的解决方案：
fwrite(string, sizeof(char), length, stdout);
Here's a sample code:
这是一个示例代码：
#include <stdio.h>
int main(void) {
size_t length = 5;
char string[length];
string[0] = 'A';
string[1] = 'B';
string[2] = 0; // null character in the middle
string[3] = 'C';
string[4] = 'D';
printf("With printf: %.*s\n", length, string);
printf("With fwrite: ");
fwrite(string, sizeof(char), length, stdout);
printf("\n");
return 0;
}
Output:
输出：
With printf: AB
With fwrite: AB CD
