用C连接字符串，哪种方法更有效？ [英] Concatenating strings in C, which method is more efficient?

问题描述

我遇到这两种方法来连接字符串：

I came across these two methods to concatenate strings:

公共部分：

char* first= "First";
char* second = "Second";
char* both = malloc(strlen(first) + strlen(second) + 2);

方法1：

strcpy(both, first);
strcat(both, " ");
strcat(both, second);

方法2：

sprintf("%s %s", first, second);

在这两种情况下的内容两个是第一第二。

In both cases the content of both would be "First Second".

我想知道哪一个是更有效的（我要执行几个串联操作），或者如果你知道一个更好的方式来做到这一点。

I would like to know which one is more efficient (I have to perform several concatenation operations), or if you know a better way to do it.

感谢您的时间。

编辑：在第一种情况的空间本来的字符串之一内的

推荐答案

有关可读性，我会去用

char * s = malloc(snprintf(NULL, 0, "%s %s", first, second) + 1);
sprintf(s, "%s %s", first, second);

如果您的平台支持GNU扩展，你也可以使用 asprintf（）：

If your platform supports GNU extensions, you could also use asprintf():

char * s = NULL;
asprintf(&s, "%s %s", first, second);

如果你坚持与MS C运行时，你必须使用 _scprintf（）来确定最终的字符串的长度：

If you're stuck with the MS C Runtime, you have to use _scprintf() to determine the length of the resulting string:

char * s = malloc(_scprintf("%s %s", first, second) + 1);
sprintf(s, "%s %s", first, second);

下面将最有可能是最快的解决方法：

The following will most likely be the fastest solution:

size_t len1 = strlen(first);
size_t len2 = strlen(second);

char * s = malloc(len1 + len2 + 2);
memcpy(s, first, len1);
s[len1] = ' ';
memcpy(s + len1 + 1, second, len2 + 1); // includes terminating null

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