Valgrind

Question

我正在尝试为自定义结构创建一个 'array of pointers'，动态分配内存，因为我不确定该数组必须具有的大小。初始化数据时，我可以毫无问题地访问每个索引处的自定义结构。

一旦我走出初始化循环，突然 valgrind 告诉我我正在使用大小为 8 的单元化值。我真的不明白为什么会这样。使用 calloc 将所有内容初始化为 null 也没有（如我所料）有帮助。使用像 FuncSym *f_sym[NB_LINES]; 这样的指针数组并更改需要更改的内容也无济于事。我确实认为 FuncSym_create(...) 正确初始化了所有内容。

...
unsigned long count = 0;
FuncSym **f_sym = (FuncSym**)malloc(NB_LINES * sizeof(FuncSym*));
unsigned long cur_max = NB_LINES;

char *line = NULL;
size_t len = 0;
ssize_t nread;
const char *del = " ";
while((nread = getline(&line, &len, tmp)) != -1) {
    if(true) { // make example smaller
        if(++count < cur_max) {
            f_sym[count] = FuncSym_create("name", 10, 10);
            printf("No Problem Here! \n Addr: %lu", FuncSym_addr(f_sym[count]));
        } else { // make sure size fits
            cur_max = 2*cur_max;
            FuncSym **tmp = (FuncSym**)realloc(f_sym, cur_max*sizeof(FuncSym*));
            if(!tmp){
                for(unsigned long i = 0; i < count; i++)
                    FuncSym_free(f_sym[i]);
                free(f_sym);
                exit(EXIT_FAILURE);
            }
            f_sym = tmp;
            f_sym[count] = FuncSym_create("name", 10, 10);
        }
    }
}
for(unsigned long i = 0; i <= count; i++){
    printf("Unitialised value here: %lu\n\n", FuncSym_addr(f_sym[i]));
}
...

struct FuncSym {
    char *name;
    unsigned long addr;
    unsigned long size;
};

FuncSym *FuncSym_create(char *sym_name, unsigned long addr, unsigned long size){
    assert(sym_name != NULL);
    FuncSym *f_sym = (FuncSym*)malloc(sizeof(FuncSym));
    if(!f_sym) stack_mem_error();
    f_sym->name = strdup(sym_name);
    f_sym->addr = addr;
    f_sym->size = size;
    return f_sym;
}
unsigned long FuncSym_addr(FuncSym *f_sym) { return f_sym->addr; }

Answer 1

f_sym[0] 从未设置，因为在输入 if 语句之前计数器已递增 (++counter)。稍后访问时 f_sym[0] 确实未初始化。固定计数器解决了所有问题。以防万一有人读到这个问题。

...
while((nread = getline(&line, &len, tmp)) != -1) {
    if(true) { // make example smaller
        if(count+1 < cur_max) {
            f_sym[count++] = FuncSym_create("name", 10, 10);
            printf("No Problem Here! \n Addr: %lu", FuncSym_addr(f_sym[count]));
        } else { // make sure size fits
            cur_max = 2*cur_max;
            FuncSym **tmp = (FuncSym**)realloc(f_sym, cur_max*sizeof(FuncSym*));
            if(!tmp){
                for(unsigned long i = 0; i < count; i++)
                    FuncSym_free(f_sym[i]);
                free(f_sym);
                exit(EXIT_FAILURE);
            }
            f_sym = tmp;
            f_sym[count++] = FuncSym_create("name", 10, 10);
        }
    }
}
...

Valgrind - 使用在堆上分配的未初始化值

Valgrind - Use of uninitialised value allocated on the heap

c

malloc

initialization

heap-memory