《C和指針》第10章習題解答：結構體定義與位域實戰

《C和指針》第10章習題解答：結構體定義與位域實戰

本章重點：結構體嵌套、位域、對齊與內存佈局。

習題 10.1：電話號碼結構體

typedef struct {
    unsigned char QuHao[5];      // 區號
    unsigned char Exchange[10];  // 局號
    unsigned char StnNum[10];    // 用戶號
} TelphoneNumber;

typedef struct {
    unsigned char date[10];
    unsigned char time[10];
    TelphoneNumber UserTelphone;
    TelphoneNumber CallTelphone;
    TelphoneNumber PayTelphone;
} Telphone_Call;

習題 10.2：銷售記錄結構體（多態銷售方式）

typedef struct { float MSRP, ActualPrice, SalesTax, LicenseFee; } CashSale;
typedef struct { float MSRP, ActualPrice, DownPayment, SecurityDeposit, MonthlyPayment; int LeaseTerm; } Rent;
typedef struct { float MSRP, ActualPrice, SalesTax, LicenseFee, DownPayment; int LoanDuration; float InterestRate, MonthlyPayment; char BankName[21]; } LoanSale;

typedef struct {
    char CustomerName[21], CustomerAddr[41], Model[21];
    CashSale CashSal;
    Rent RentSal;
    LoanSale LoanSal;
} SaleRecord;

習題 10.3：機器指令位域結構（PDP-11 風格）

typedef struct { unsigned int dst_reg:3, dst_mode:3, opcode:10; } SingleOperat;
typedef struct { unsigned int dst_reg:3, dst_mode:3, src_reg:3, src_mode:3, opcode:4; } DoubleOperat;
typedef struct { unsigned int offset:8, opcode:8; } Branch;
typedef struct { unsigned int dst_reg:3, dst_mode:3, src_reg:3, opcode:7; } RegistSrc;
typedef struct { unsigned int opcode:16; } MiscCmd;

typedef struct {
    unsigned short addr;
    SingleOperat sgl_op;
    DoubleOperat dbl_op;
    Branch branch;
    RegistSrc reg_src;
    MiscCmd misc;
} machine_inst;

位域自動打包進整數單元，順序視實現定義（通常從低位到高位），跨平台移植需注意端序與填充規則。