【发布时间】：2017-04-05 09:51:28
【问题描述】：
我正在尝试构建一个用作汇编程序的程序，它将获取文件名作为命令行参数并将它们转换为机器代码。
程序编译得很好，使用 1 个文件名运行正常，但是当我尝试使用多个文件名运行时，第一次迭代后出现错误。
我认为Clear() 函数可能有问题（它会清除上一次迭代中分配的所有数据），但不确定原因。请注意，这是部分内容，但正如我所说，除非使用多个文件，否则程序将运行。
struct symbolStruct { // a structure which is used to absorb info about a tag, its place in memory and related flags
char *name;
int place;
unsigned int isEntry : 1;
unsigned int isData : 1;
unsigned int isExternal : 1;
struct symbolStruct *next;
};
typedef struct { // a structure which is used to absorb info about the operand structure of an instruction line
unsigned int numOfOperands : 2;
unsigned int addrMethSou : 2;
unsigned int addrMethDest : 2;
unsigned int operation : 4;
unsigned int extraWords : 2;
char *firstOperand;
char *secondOperand;
} OperandType;
typedef struct {
unsigned int row : WORD_SIZE;
} int15;
struct MachineCode { // a structure which is used to absorb machine code lines, and their location in the assembly file
unsigned int row : WORD_SIZE;
unsigned int line;
OperandType *structure;
struct MachineCode *next;
};
struct DataCode { // a structure which is used to absorb data and string elements (signed numbers and ascii characters)
unsigned int row : WORD_SIZE;
struct DataCode *next;
};
struct Operation { /* the main operation structure, contains pointers to all used lists, the ic and dc counters, the
current line number which is dealt with and the error flag. */
unsigned int ic;
unsigned int dc;
struct symbolStruct *externHead; // a pointer to a linked list of extern tags used in the assembly file, and their locations
struct symbolStruct *symbolHead; // a pointer to a linked list of all tags
struct DataCode *dataHead; // a pointer to a linked list of all data/string elements
struct MachineCode *machineHead; // a pointer to a linked list of all machine code rows
int linenumber;
unsigned int errorflag : 1; // raised in case of an error which triggered a warning
};
#include "header.h"
void FirstRun(struct Operation*, char *);
void DataUpdate(struct symbolStruct*,int);
void SecondRun(struct Operation *, char *);
void Clear(struct Operation *);
int main(int argc, char *argv[]) {
int i;
struct Operation programCore = {0,0,NULL,NULL,NULL,NULL,0,0};
for(i=1;i<argc;i++) {
char *fn = argv[i];
FirstRun(&programCore,fn);
DataUpdate(programCore.symbolHead,programCore.ic+INSTRUCTION_OFFSET);
SecondRun(&programCore,fn);
Clear(&programCore);
programCore.symbolHead = programCore.externHead = programCore.dataHead = programCore.machineHead = NULL;
}
if(argc < 2) {
fprintf(stderr,"No files selected.\n");
}
return 0;
}
/*Used to empty the linked lists and allocated memory after the program has finished one iteration. */
void Clear(struct Operation *programCore) {
/*f(pointer name) is there to hold a pointer to the allocated memory which is about to be flushed. */
struct MachineCode *machineHead = programCore->machineHead, *fMachineHead;
struct DataCode *dataHead = programCore->dataHead, *fDataHead;
struct symbolStruct *externHead = programCore->externHead, *fExternHead;
struct symbolStruct *symbolHead = programCore->symbolHead, *fSymbolHead;
while(machineHead != NULL) {
fMachineHead = machineHead;
machineHead = machineHead->next;
if(fMachineHead->structure != NULL) {
if(fMachineHead->structure->numOfOperands == 2)
free(fMachineHead->structure->secondOperand);
if(fMachineHead->structure->numOfOperands > 0)
free(fMachineHead->structure->firstOperand);
free(fMachineHead->structure);
}
free(fMachineHead);
}
while(dataHead != NULL) {
fDataHead = dataHead;
dataHead = dataHead->next;
free(fDataHead);
}
while(externHead != NULL) {
fExternHead = externHead;
externHead = externHead->next;
free(fExternHead->name);
free(fExternHead);
}
while(symbolHead != NULL) {
fSymbolHead = symbolHead;
symbolHead = symbolHead->next;
free(fSymbolHead->name);
free(fSymbolHead);
}
programCore->ic = programCore->dc = programCore->linenumber = programCore->errorflag = 0;
}
【问题讨论】：
-
你还没有说你的代码在哪里崩溃——在调试器中运行它，你会看到它发生在哪一行。也可能会向您展示您需要修复的内容。
-
[off-topic] 就个人而言，我会使用（可变大小）数组，而不是表的链接列表。
-
为了便于阅读和理解：1) 通过一个空行分隔代码块（for、if、else、while、do...while、switch、case、default）。 2) 用 2 或 3 个空行分隔函数（保持一致） 3) 遵循公理：每行只有一个语句，并且（最多）每个语句一个变量声明。
-
虽然“隐式转换”功能可以节省代码，但不应依赖它。 NULL 和 0 的含义有很大的不同（尽管位值可能相同。
-
当命令行参数有问题时，（比如没有）代码应该输出
USAGE语句到stderr，类似：fprintf( stderr, "USAGE: %s <srcFileName1> [[srcFileNameN]]\n", argv[0] );这样的语句通常后面跟着exit( EXIT_FAILURE );
标签： c linux struct error-handling segmentation-fault