问题
I am studying the C language.
When I pass a pointer to gets(), I find it can work well.
char *ptr;
gets(ptr);
puts(ptr);
But if I define an array of pointers, it doesn't work.
char *ptr[4];
int i=0;
for(i=0;i<4;++i)
gets(ptr[i]);
for(i=0;i<4;++i)
puts(ptr[i]);
Are they different, or is the first part wrong in fact? I want to know the reason.
回答1:
You pass a pointer to a function (e.g. gets()
) that writes data to a memory location pointed by your pointer. In your case, you have the uninitialized pointer, which means it points to a random memory location (where applications or an operating system resides). This leads to random effects - from "working" to abnormal termination or hanging. You need to reserve memory and assign pointer to point there, e.g. by:
char *ptr = (char*)malloc(256);
gets(ptr);
puts(ptr);
free(ptr);
Consider to use gets_s()
that is more secure.
回答2:
char *ptr[4];
int i=0;
for(i=0;i<4;++i)
gets(ptr[i]);
This is not valid C code as you did not allocate space for ptr[i]
. On the other hand, never use gets
because it's a function that does not check for buffer limit.
回答3:
The pointer has to point somewhere first.
#define BUFSIZE 100
char *ptr = malloc(BUFSIZE);
fgets(stdin, ptr, BUFSIZE);
puts(ptr);
char *ptr[4];
int i=0;
for(i=0;i<4;++i) {
ptr[i] = malloc(BUFSIZE);
fgets(ptr[i], BUFSIZE, stdin);
}
for(i=0;i<4;++i) {
puts(ptr[i]);
}
来源:https://stackoverflow.com/questions/60650328/can-i-use-a-pointer-as-the-parameter-of-gets-in-c