Very interesting question, and clever trick. Let’s look at a simple example of getting a single byte manipulated. Using unsigned 8 bit for simplicity. Imagine your number is xxaxxbxx and you want ab000000. The solution consisted of two steps: a bit masking, followed by multiplication. The bit mask is a simple AND operation that turns … Read more
Exactly what it sounds like, assuming you’re used to the abbreviated way in which C and UNIX assigns words, it duplicates strings 🙂 Keeping in mind it’s actually not part of the current (C17) ISO C standard itself(a) (it’s a POSIX thing), it’s effectively doing the same as the following code: char *strdup(const char *src) … Read more
If you don’t want to change the strings, then you could simply do const char *a[2]; a[0] = “blah”; a[1] = “hmm”; When you do it like this you will allocate an array of two pointers to const char. These pointers will then be set to the addresses of the static strings “blah” and “hmm”. … Read more
As Douglas Mayle noted, it basically denotes a type name. Consequently, you would be ill-advised to end variable or function names with ‘_t‘ since it could cause some confusion. As well as size_t, the C89 standard defines wchar_t, off_t, ptrdiff_t, and probably some others I’ve forgotten. The C99 standard defines a lot of extra types, … Read more
See the C FAQ, Question 1.32 Q: What is the difference between these initializations? char a[] = “string literal”; char *p = “string literal”; My program crashes if I try to assign a new value to p[i]. A: A string literal (the formal term for a double-quoted string in C source) can be used in … Read more
You can escape it by posting a double ‘%’ like this: %% Using your example: printf(“hello%%”); Escaping the ‘%’ sign is only for printf. If you do: char a[5]; strcpy(a, “%%”); printf(“This is a’s value: %s\n”, a); It will print: This is a’s value: %%
Bus errors are rare nowadays on x86 and occur when your processor cannot even attempt the memory access requested, typically: using a processor instruction with an address that does not satisfy its alignment requirements. Segmentation faults occur when accessing memory which does not belong to your process. They are very common and are typically the … Read more
mmap is great if you have multiple processes accessing data in a read only fashion from the same file, which is common in the kind of server systems I write. mmap allows all those processes to share the same physical memory pages, saving a lot of memory. mmap also allows the operating system to optimize … Read more
As noted in other answers, the problem is that you use gcc with no compiler options set. If you do this, it defaults to what is called “gnu90”, which is a non-standard implementation of the old, withdrawn C90 standard from 1990. In the old C90 standard there was a major flaw in the C language: … Read more
Perhaps the simplest solution uses one of my favorite little-known functions, strcspn(): buffer[strcspn(buffer, “\n”)] = 0; If you want it to also handle ‘\r’ (say, if the stream is binary): buffer[strcspn(buffer, “\r\n”)] = 0; // works for LF, CR, CRLF, LFCR, … The function counts the number of characters until it hits a ‘\r’ or … Read more