c语言第5章：异常处理

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李延 LV6 2022-05-20

悬赏：20积分

# 1 说明

在c语言中，模仿java 写一个通过try-catch 以及 Throw 的一个异常机制。如下：

```c
TRY
    run();  // 执行自己的方法
CATCH(&ex1)
    printf("发生异常ex1\n"); // 捕获到一个异常
CATCH(&ex2)
    printf("发生异常ex2\n"); // 捕获到一个异常
FINILLY
     printf("执行finally\n"); // 执行finilly
     ENDTRY

```

同时通过Throw 抛出异常

```c
int run(Exception *exception) {
    Throw(exception);
    return 0;
}
```

# 2 原理

首先我们所有的try、catch等命令都是通过宏定义进行的.

对于异常的调整通过setjmp.h 的 longjmp和setjmp 函数，实现异常发生时的跳转。

# 3 实现

## 3.1 except.h

```c
#ifndef EXCEPTION
#define EXCEPTION

#include <setjmp.h>
#include <pthread.h>
#include "stdlib.h"
#include "assert.h"

#define EXCEPTION_ERROR 1 //发生异常标记
#define EXCEPTION_OK 0 //未异常标记

pthread_key_t key;
/// 异常定义
typedef struct {
    const char *reason;
} Exception;

typedef struct Try_module_stack {
    struct Try_module_stack *tryModuleStack;
    struct Error_msg *errorMsg;
    int Exception_type;
    int finally_type;
    jmp_buf except_jmpBuf;

} Try_module_stack;

typedef struct Error_msg {
    Exception *exception;
    const char *_File;   //异常代码文件行数
    unsigned _Line; //异常 行数

} Error_msg;

void throwFunction(Exception *exception, const char *_File, unsigned _Line);

void printfError(Error_msg *msg);

/// 可能抛出异常的代码块
#define TRY     \
do {\
    int except_type;\
    Try_module_stack *tryModuleStack = pthread_getspecific(key);\
    Try_module_stack *newTryModuleStack = (Try_module_stack *) malloc(sizeof(Try_module_stack));\
    newTryModuleStack->errorMsg = NULL;\
    Error_msg msg;\
    pthread_setspecific(key, newTryModuleStack);\
    if (tryModuleStack != NULL) {\
        newTryModuleStack->tryModuleStack = tryModuleStack;\
    } else {\
    newTryModuleStack->tryModuleStack = NULL;\
    }\
    except_type = setjmp(newTryModuleStack->except_jmpBuf);\
    if (newTryModuleStack->errorMsg != NULL) {\
        msg = *newTryModuleStack->errorMsg;\
    }\
    if (except_type == 0) {

#define ENDTRY          \
    }\
    int exception_type = newTryModuleStack->Exception_type;\
    Try_module_stack *old = newTryModuleStack->tryModuleStack;\
    if (old == NULL) {\
        pthread_key_delete(key);\
    } else {\
        pthread_setspecific(key, old);\
    }\
    if (newTryModuleStack->errorMsg != NULL) {\
        free(newTryModuleStack->errorMsg);\
    }\
    free(newTryModuleStack);\
    if (exception_type == -2) {\
        longjmp(tryModuleStack->except_jmpBuf, EXCEPTION_ERROR);\
    }else                        \
    if (exception_type == -4) {\
        printfError(&msg); \
        assert(0);\
    }    \
} while (0);

/// 捕获特定异常
#define CATCH(ex)      \
    } else if (newTryModuleStack->Exception_type == -1 && newTryModuleStack->errorMsg->exception == &ex1) {

#define DEFCATCH    \
    } else if (newTryModuleStack->Exception_type == -1 ) {

#define FINILLY \
    }\
    if (newTryModuleStack->finally_type != 1) {\
    newTryModuleStack->finally_type = 1;

/// 抛出异常
#define Throw(exception) throwFunction(exception, __FILE__, __LINE__)

#endif /* __EXCEPION_H__ */
```

## 3.2 except.c

```c
#include "except.h"
#include "stdio.h"

void throwFunction(Exception *exception, const char *_File, unsigned _Line) {
    Try_module_stack *tryModuleStack = pthread_getspecific(key);
    Error_msg *msg = (Error_msg *) malloc(sizeof(Error_msg));
    msg->exception = exception;
    msg->_File = _File;
    msg->_Line = _Line;
    if (tryModuleStack != NULL) {

if (tryModuleStack->errorMsg != NULL && tryModuleStack->tryModuleStack != NULL) {
            tryModuleStack->Exception_type = -2;
            tryModuleStack->tryModuleStack->errorMsg = msg;
            tryModuleStack->tryModuleStack->Exception_type = -1;
        } else if (tryModuleStack->tryModuleStack == NULL) {
            tryModuleStack->Exception_type = -4;
            tryModuleStack->errorMsg = msg;
        } else if (tryModuleStack->errorMsg != NULL) {
            tryModuleStack->Exception_type = -3;
            tryModuleStack->errorMsg = msg;
        } else {
            tryModuleStack->Exception_type = -1;
            tryModuleStack->errorMsg = msg;
        }
        longjmp(tryModuleStack->except_jmpBuf, EXCEPTION_ERROR);

} else {
        printfError(msg);
        assert(0);
    }
}

void printfError(Error_msg *msg) {
    printf("has error :[%s], at  : [%s] in [%d]\n", msg->exception->reason, msg->_File, msg->_Line);
}
```

# 4 测试类

```c
#include "../except/except.h"
#include "stdio.h"

Exception ex1 = {"ex1"};
Exception ex2 = {"ex2"};
Exception ex3 = {"ex3"};
Exception ex4 = {"ex4"};

int run(Exception *exception) {
    Throw(exception);
    return 0;
}

void run2(Exception *exception) {

TRY
            run(exception);
        CATCH(&ex1)
            printfError(&msg);
            Throw(exception);
        CATCH(&ex2)
            printfError(&msg);
        FINILLY
            printf("执行finally\n");
            ENDTRY
}

void ExceptionTest(Exception *exception) {

TRY
            run2(exception);
        CATCH(&ex1)
            printfError(&msg);
        CATCH(&ex2)
            printfError(&msg);
        FINILLY
            printf("执行finally\n");
            Throw(exception);
            ENDTRY

}

int main() {

ExceptionTest(&ex1); // 异常1
    ExceptionTest(&ex2); // 异常2
    ExceptionTest(&ex3); // 异常3
    ExceptionTest(&ex4); // 异常4
    return 0;
}
```

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