使用编译环境是qt 写第程序：

需要注意的是字符串后面有一个结束字符'\0，因此需要减一，底下没有减一出现异常情况,当然你还可以使用strlen，这时候就可以不用减1了，strlen从字符串的开头位置依次向后计数，直到遇见\0，然后返回计时器的值。最终统计的字符串长度不包括\0

    char ch1[] = "1234567890";
    char ch2[] = "abcdefghij";
    char ch3[] = "klmnopqrst";
    char ch4[256] = {0};

    memcpy(ch4,ch1,sizeof(ch1));
    qDebug()<<"1 ch4 = "<<QString(ch4);
    memcpy(ch4+sizeof(ch1),ch2,sizeof(ch2));
    qDebug()<<"2 ch4 = "<<QString(ch4);
    memcpy(ch4+sizeof(ch1) + sizeof(ch3),ch3,sizeof(ch3));
    qDebug()<<"3 ch4 = "<<QString(ch4);
输出：
1 ch4 =  "1234567890"
2 ch4 =  "1234567890"
3 ch4 =  "1234567890"

减一后再打印输出如下：

    char ch1[] = "1234567890";
    char ch2[] = "abcdefghij";
    char ch3[] = "klmnopqrst";
    char ch4[256] = {0};

    memcpy(ch4,ch1,sizeof(ch1));
    qDebug()<<"1 ch4 = "<<QString(ch4);
    memcpy(ch4+sizeof(ch1)-1,ch2,sizeof(ch2));
    qDebug()<<"2 ch4 = "<<QString(ch4);
    memcpy(ch4+sizeof(ch1)-1 + sizeof(ch3)-1,ch3,sizeof(ch3));
    qDebug().noquote()<<"3 ch4 = "<<QString(ch4);

输出为
1 ch4 =  "1234567890"
2 ch4 =  "1234567890abcdefghij"
3 ch4 =  "1234567890abcdefghijklmnopqrst"