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#define SRC_ASCLIN_ASCLIN0_RX (*(volatile Ifx_SRC_SRCR*)0xF0038084u)
Here SRC_ASCLIN_ASCLIN0_RX means ASCLIN(Async/Sync serial LIN Comm) Receive Service Request.
I know that the macro is used to point at the address 0xF0038084u. But I want real time examples.
Am working on UART development on Infineon microcontroller.
The macro, when expanded by the preprocessor, cast the integer literal as an address, a pointer to Ifx_SRC_SRCR, then dereferences the pointer so you can get or set the value of the memory stored at that specific address.
So you could write e.g.
Ifx_SRC_SRCR value = SRC_ASCLIN_ASCLIN0_RX;
or
SRC_ASCLIN_ASCLIN0_RX = some_other_value;
It basically equivalent to doing e.g.
int an_integer = 6;
int *pointer_to_an_integer = &an_integer;
*pointer_to_an_integer = 10; // Equivalent to SRC_ASCLIN_ASCLIN0_RX = some_other_value above
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I have some materials showing this code. what does code means by making these assignments?
char inputfilename[128];
inputfilename[0] = 0;
char *argv[128];
*argv[1] = 0;
In C, character arrays are terminated by a null character (value 0). In both cases in your example, the code initializes the strings to "empty" (with a terminator in the first element). This would prove useful in any subsequent string operations (strcat, strcpy, etc.).
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Suppose you have the variable int num and the pointer int* cell. Does it make a difference for the values stored in cell and num to write cell = &num or *cell = num?
cell = &num
means that the contents/value of cell will be equal to the address of num.
*cell = num
means that the content at the address stored in cell, that is the value to which the pointer is pointing to, will be equal to the value of num.
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How can a string like "EINVAL" be converted into EINVAL?
I have to convert a lot of macro string to their value, what can be done?
Here is the simplest method I can think of:
#include <errno.h>
if (!strcmp(str, "EINVAL"))
value = EINVAL;
No preprocessor trick can convert the string literal to the corresponding symbol.
But you can use the preprocessor to simplify a sequence of such tests:
value = 0;
#define conv(s) do { if (!strcmp(str, #s)) value = s; } while (0)
conv(EINVAL);
conv(ENOMEM);
conv(ERANGE);
conv(EINTR);
#undef conv
A usual, be careful with the preprocessor...
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an interview question on glassdoor is as follows. With my knowledge, it is hard to deduce anything out of it. What could be an appropriate question?
A macro that computes a size_t number. Putting in a loop, it casts -1
to a size_t number, making the loop impossible to start.
as suggested by Michael Aaron Safyan, following might be the case
operates in the reverse:
for (size_t i = 0; i > ((size_t) -1); i--) {}
For explanation see the answer
The issue is that size_t is unsigned, so casting -1 to it will produce the maximum-valued size_t. One would fix this case by using a signed type (such as int or ssize_t).
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In C I wish to create a data type (like int or float) that has only 1byte. How can I possible do this? I've tried with malloc() but didn't work that way I tried.
Could you please give me a hand here?
Example:
sizeof(int) = 4 bytes
sizeof(char) = 1 byte
sizeof(float) = 4 bytes
sizeof(myDataType) = 1 byte
There is such data type. char is always guaranteed to be one byte long. If you want another name for that type, just use typedef and create a new type based on char.
More detailed explanation can be found in this question: Are there machines, where sizeof(char) != 1, or at least CHAR_BIT > 8?