perl -le 'print "aa" =~ /aaaa/'

这是执行此操作的等效PCRE代码.

$cat partial.c 
#include <stdio.h>
#include <pcre.h>

int main(void)
{
    const char *errptr;
    int erroffset,result;
    pcre *re;

    re = pcre_compile("aaaa",&errptr,&erroffset,NULL);
    if (re == NULL)
        return 42;

    result = pcre_exec(re,NULL,"aa",2,PCRE_PARTIAL,0);

    printf("%d\n",result == PCRE_ERROR_PARTIAL);

    return 0;
}

$make partial LDFLAGS=-lpcre
cc   -lpcre  partial.c   -o partial

$./partial 
1

编辑：pcretest工具可用于演示部分匹配和非部分匹配之间的区别.还包括在评论中匹配@revo建议的正则表达式的结果.

$pcretest
PCRE version 8.41 2017-07-05

  re> /aaaa/

data> aa
No match

data> aa\P
Partial match: aa
data> aaaa
 0: aaaa

$pcretest
PCRE version 8.41 2017-07-05

  re> /aaa?a?/

data> aa
 0: aa

data> aa\P
 0: aa