Problem with pointers and getstring function
- by volting
I am trying to write a function to get a string from the uart1. Its for an embedded system so I don't want to use malloc.
The pointer that is passed to the getstring function seems to point to garbage after the gets_e_uart1() is called. I don't use pointers too often so I'm sure it is something really stupid and trivial that Im doing wrong.
Regards,
V
int main()
{
char *ptr = 0;
while(1)
{
gets_e_uart1(ptr, 100);
puts_uart1(ptr);
}
return 0;
}*end main*/
//-------------------------------------------------------------------------
//gets a string and echos it
//returns 0 if there is no error
char getstring_e_uart1(char *stringPtr_, const int SIZE_)
{
char buffer_[SIZE_];
stringPtr_ = buffer_;
int start_ = 0, end_ = SIZE_ - 1;
char errorflag = 0;
/*keep geting chars until newline char recieved*/
while((buffer_[start_++] = getchar_uart1())!= 0x0D)
{
putchar_uart1(buffer_[start_]);//echo it
/*check for end of buffer
wraparound if neccesary*/
if(start_ == end_)
{
start_ = 0;
errorflag = 1;
}
}
putchar_uart1('\n');
putchar_uart1('\r');
/*check for end of buffer
wraparound if neccesary*/
if(start_ == end_)
{
buffer_[0] = '\0';
errorflag = 1;
}
else
{
buffer_[start_++] = '\0';
}
return errorflag;
}
Update:
I decided to go with approach of passing a pointer an array to the function. This works nicely, thanks to everyone for the informative answers.
Updated Code:
//-------------------------------------------------------------------------
//argument 1 should be a pointer to an array,
//and the second argument should be the size of the array
//gets a string and echos it
//returns 0 if there is no error
char getstring_e_uart1(char *stringPtr_, const int SIZE_)
{
char *startPtr_ = stringPtr_;
char *endPtr_ = startPtr_ + (SIZE_ - 1);
char errorflag = 0;
/*keep geting chars until newline char recieved*/
while((*stringPtr_ = getchar_uart1())!= 0x0D)
{
putchar_uart1(*stringPtr_);//echo it
stringPtr_++;
/*check for end of buffer
wraparound if neccesary*/
if(stringPtr_ == endPtr_)
{
stringPtr_ = startPtr_;
errorflag = 1;
}
}
putchar_uart1('\n');
putchar_uart1('\r');
/*check for end of buffer
wraparound if neccesary*/
if(stringPtr_ == endPtr_)
{
stringPtr_ = startPtr_;
*stringPtr_ = '\0';
errorflag = 1;
}
else
{
*stringPtr_ = '\0';
}
return errorflag;
}
