C语言主存分配与回收算法代码详解及优化

void reclaim(char J) { int i, k, j, s, t, p; float S, L; // 寻找已分配区表中对应登记项 s = point.uhead; t = s; if (s == -1) { cout << '没有找到该作业\n' << endl; return; } while (s != -1) { if (usetable[s].uname == J && s < n) { p = t; k = s; break; } t = s; s = usetable[s].next; } s = k; if (s == -1) { cout << '没有找到该作业\n' << endl; return; } if (s >= n) { // 在已分配区表中找不到名字为J的作业 cout << '找不到该作业' << endl; return; } // 修改已分配区表 usetable[s].flag = '空表目'; usetable[s].uname = ''; // 取得归还分区的起始地址S和长度L S = usetable[s].address; L = usetable[s].length; usetable[s].address = 0; usetable[s].length = 0; //usetable[s].next = -1; if (s == point.uhead) { point.uhead = usetable[s].next; usetable[s].next = -1; if (s == point.utail) point.utail = p; usetable[p].next = -1; } else if (s != point.uhead && s != point.utail) { usetable[p].next = usetable[s].next; usetable[s].next = -1; } else { usetable[s].next = -1; } // 寻找回收分区的上下邻空闲区，上邻表目k,下邻表目j j = -1; k = -1; i = 0; while (i < m && (j == -1 || k == -1)) { if (freetable[i].flag == '可用') { if (retable[i].address + freetable[i].length == S) k = i; // 找到上邻 if (freetable[i].address == S + L) j = i; // 找到下邻 i++; } } if (k != -1) { if (j != -1) { // 上邻空闲区，下邻空闲区,三项合并 freetable[k].length = freetable[j].length + freetable[k].length + L; freetable[k].flag = '可用'; freetable[k].fname = ''; freetable[j].length = freetable[j].address = 0; freetable[j].fname = ''; } else if (freetable[k].flag != '可用') { // 上邻非空闲区，下邻为空闲区，与下邻合并 freetable[k].length = freetable[k].length + L; freetable[k].fname = ''; } } else if (j != -1) { freetable[j].address = S; freetable[j].length = freetable[j].length + L; freetable[j].fname = ''; } else { // 上下邻均为非空闲区,回收区域直接填人 // 在空闲区表中寻找空栏目 t = 0; while (freetable[t].flag == '可用' && t < m) t++; if (t >= m) { // 空闲区表满,回收空间失败,将已分配区表复原 cout << '主空闲表没有空闲空间回收失败' << endl; return; } freetable[t].address = S; freetable[t].length = L; freetable[t].flag = '可用'; freetable[t].fname = ''; freetable[point.ftail].next = t; point.ftail = t; freetable[t].next = -1; } }

void main() { char name; float xk; // 空闲区表初始化 freetable[0].address = 10240; // 假定空闲区表内存起始地址 freetable[0].length = 102400; // 假定空闲区表的空间大小 freetable[0].flag = '可用'; freetable[0].next = -1; int i, a; point.uhead = point.utail = -1; point.fhead = 0; point.ftail = 0; for (i = 1; i < m; i++) { freetable[i].flag = '空表目'; freetable[i].length = 0; freetable[i].address = 0; freetable[i].uname = ''; freetable[i].next = -1; } // 已分配区表初始化 for (i = 0; i < n; i++) { usetable[i].flag = '空表目'; usetable[i].length = 0; usetable[i].address = 0; usetable[i].uname = ''; usetable[i].next = -1; } while (1) { cout << endl << '选择功能项(0-退出,1-分配主存,2-回收主存,3-显示主存)' << endl; cout << '选择功能项(0-3):'; cin >> a; switch (a) { case 0: exit(0); // a=0程序结束 break; case 1: // a=1分配主存空间 cout << '输入作业名和作业所需长度:'; cin >> name >> xk; allocate(name, xk); break; case 2: // a=2回收主存空间 cout << '输入要回收的作业名:'; cin >> name; reclaim(name); // 回收主存空间 break; case 3: // a=3显示主存情况输出空闲区表和已分配区表 cout << endl << '输出空闲表区:\n项名 起始地址 分区长度 标志\n'; i = point.fhead; while (i != -1 && i < m) { cout << setiosflags(ios::left) << setw(7) << i << setw(8) << setiosflags(ios::left) << freetable[i].address << setw(8) << setiosflags(ios::left) << freetable[i].length << setw(8) << setiosflags(ios::left) << freetable[i].flag << endl; i = freetable[i].next; } cout << endl << '输出已分配区表:\n'; cout << '项名 起始地址 分区长度 标志\n'; i = point.uhead; while (i != -1 && i < n) { cout << setiosflags(ios::left) << setw(7) << usetable[i].uname << setw(8) << setiosflags(ios::left) << usetable[i].address << setw(8) << setiosflags(ios::left) << usetable[i].length << setw(8) << setiosflags(ios::left) << usetable[i].flag << endl; i = usetable[i].next; } break; default: cout << '没有这个选项' << endl; break; } }