[SOLVED] A question about pointers in C...

trist007 · 07-10-2011, 09:01 PM

char *strerror(int errnum);

This function basically takes errno(int) and returns a pointer to a string describing the error.

So shouldn't this work?

Code:

char buf[32];
buf = strerror(13);
printf("error: %s\n", buf);

Yet gcc "returns incompatible types in assignment" for the 2nd line.

Isn't 'buf' by itself a char pointer? It's the same as *(buf+0) or &buf[0] no?

dwhitney67 · 07-10-2011, 09:15 PM

Quote:

Originally Posted by trist007

Isn't 'buf' by itself a char pointer?

No, buf is declared as an array of char.

strerror() returns a char*; thus you should declare buf to be a char*. The area in memory that strerror() returns quite possibly is a statically declared buffer of N bytes. Thus the callee (that would be your program) should assign a pointer to that buffer. You cannot assign a char* to an array, although you can copy the string data using functions such as strcpy() or sprintf().

Anyhow, consider the following:

Code:

char array[30];

char* a = array;

Above, 'a' is pointing to the first byte (char) of the array. If you still have questions about the differences between pointers and arrays, I would suggest that you revisit your C reference book.

chrism01 · 07-11-2011, 01:10 AM

It often helps to firmly remember

Code:

# type 'ptr-to-char'
char *p;

# type 'array-of-char'
char b[3];

# strictly speaking, there is no such thing as a 'string' type in C,
# instead it's a specially handled 'array-of-char' that needs '\0'
# as the last item to be usable by most 'string' fns

HTH

trist007 · 07-11-2011, 10:20 PM

great ty