memccpy

从 src 所指向的对象复制字节到 dest 所指向的对象，当满足以下任一条件时停止：

• 复制 count 个字节
• 找到（并复制）字节 ( unsigned char ) c

src 和 dest 对象将被解释为 unsigned char 类型的数组。

当满足以下 任意 条件时，其行为是未定义的：

• 访问超出 dest 数组末尾；
• 对象存在重叠（这违反了 restrict 约定）
• dest 或 src 是无效指针或空指针

参数

返回值

如果找到了字节 ( unsigned char ) c ， memccpy 将返回指向 dest 中 ( unsigned char ) c 之后下一个字节的指针。否则返回空指针。

注释

该函数与 POSIX memccpy 完全相同。

memccpy ( dest, src, 0 , count ) 的行为类似于 strncpy ( dest, src, count ) ，不同之处在于前者返回指向写入缓冲区 末尾 的指针，并且不会用零填充目标数组。因此， memccpy 对于高效连接多个字符串非常有用。

char bigString[1000];
char* end = bigString + sizeof bigString;
char* p = memccpy(bigString, "John, ", '\0', sizeof bigString - 1);
if (p)
    p = memccpy(p - 1, "Paul, ", '\0', end - p);
if (p)
    p = memccpy(p - 1, "George, ", '\0', end - p);
if (p)
    p = memccpy(p - 1, "Joel ", '\0', end - p);
if (!p)
    end[-1] = '\0';
puts(bigString); // John, Paul, George, Joel

示例

#include <ctype.h>
#include <stdio.h>
#include <string.h>
int main(void)
{
    const char src[] = "Stars: Altair, Sun, Vega.";
    const char terminal[] = {':', ' ', ',', '.', '!'};
    char dest[sizeof src];
    const char alt = '@';
    for (size_t i = 0; i != sizeof terminal; ++i)
    {
        void* to = memccpy(dest, src, terminal[i], sizeof dest);
        printf("Terminal '%c' (%s):\t\"", terminal[i], to ? "found" : "absent");
        // if `terminal` character was not found - print the whole `dest`
        to = to ? to : dest + sizeof dest;
        for (char* from = dest; from != to; ++from)
            putchar(isprint(*from) ? *from : alt);
        puts("\"");
    }
    puts("\n" "Separate star names from distances (ly):");
    const char *star_distance[] = {
        "Arcturus : 37", "Vega : 25", "Capella : 43", "Rigel : 860", "Procyon : 11"
    };
    char names_only[64];
    char *first = names_only;
    char *last = names_only + sizeof names_only;
    for (size_t t = 0; t != (sizeof star_distance) / (sizeof star_distance[0]); ++t)
    {
        if (first)
            first = memccpy(first, star_distance[t], ' ', last - first);
        else
            break;
    }
    if (first)
    {
        *first = '\0';
        puts(names_only);
    }
    else
        puts("Buffer is too small.");
}

Terminal ':' (found):   "Stars:"
Terminal ' ' (found):   "Stars: "
Terminal ',' (found):   "Stars: Altair,"
Terminal '.' (found):   "Stars: Altair, Sun, Vega."
Terminal '!' (absent):  "Stars: Altair, Sun, Vega.@"
Separate star names from distances (ly):
Arcturus Vega Capella Rigel Procyon

参见