完整披露:这是我第一次在C中进行任何重要编程,也是我在堆栈溢出上的第一篇文章。
我正在研究最终将与野牛一起使用的代码,以实现计划/球拍语言的一小部分。所有这些代码都在一个C文件中。我有三个结构:Binding
,Lambda
和SymbolEntry
。我还没有使用Lambda
结构,它只是为了完整。我也有一个符号表,该表包含符号条目。 printSymbolTable()
完全执行该名称所暗示的内容:
typedef struct
{
char* name;
char* value;
} Binding;
typedef struct
{
int numBindings;
Binding** bindings;
char* functionBody;
} Lambda;
typedef struct
{
Binding* binding;
Lambda* function;
} SymbolEntry;
SymbolEntry* symbolTable = NULL;
int numSymbols = 0;
void printSymbolTable()
{
if (symbolTable)
{
int i = 0;
for (i; i < numSymbols; i++)
{
printf("tsymbolTable[%i]: %s = %sn", i, symbolTable[i].binding->name, symbolTable[i].binding->value);
}
}
}
我目前正在尝试确定定义和查找变量的逻辑。相关功能:
// Takes a name and an exprssion and stores the result in the symbol table
void defineVar(char* name, char* expr)
{
printf("nSetting %s = %sn", name, expr);
printf("Previous number of symbols: %in", numSymbols);
Binding props;
props.name = name;
props.value = expr;
SymbolEntry entry;
entry.binding = &props;
entry.function = NULL;
symbolTable = realloc(symbolTable, sizeof(SymbolEntry) * ++numSymbols);
if (!symbolTable)
{
printf("Memory allocation failed. Exiting.n");
exit(1);
}
symbolTable[numSymbols - 1] = entry;
printf("New number of symbols: %in", numSymbols);
printf("defineVar result:n");
printSymbolTable();
}
// Test storing and looking up at least 4 variables, including one that is undefined
void testVars()
{
printf("Variable testsn");
defineVar("foo", "0");
printf("After returning from defineVar:n");
printSymbolTable();
defineVar("bar", "20");
printf("After returning from defineVar:n");
printSymbolTable();
}
main()
调用testVars()
。编译时我没有任何警告或错误,并且该程序成功执行。但是,这就是结果:
Variable tests
Setting foo = 0
Previous number of symbols: 0
New number of symbols: 1
defineVar result:
symbolTable[0]: foo = 0
After returning from defineVar:
symbolTable[0]: 1�I��^H��H���PTI��@ = �E
Setting bar = 20
Previous number of symbols: 1
New number of symbols: 2
defineVar result:
symbolTable[0]: bar = 20
symbolTable[1]: bar = 20
After returning from defineVar:
symbolTable[0]: 1�I��^H��H���PTI��@ = �E
symbolTable[1]: 1�I��^H��H���PTI��@ = �E���
在defineVar()
函数之外,我不仅会获得垃圾值,而且定义bar
的调用也显示不正确的非junk值。我不确定我在做什么错,但我认为这可能是realloc()
的东西。但是,在将字符串解析为单个令牌时,类似的策略也有效,因此这就是我试图效仿的。我在做什么错?
,因为它指向变量(或变量 - 至少props
,没有进一步读取)函数本地的本地读取,并且返回后堆栈帧被丢弃(并很快覆盖)。