From man gcc -fno-builtin -fno-builtin-function Don’t recognize built-in functions that do not begin with __builtin_ as prefix. GCC normally generates special code to handle certain built-in functions more efficiently; for instance, calls to “alloca” may become single instructions which adjust the stack directly, and calls to “memcpy” may become inline copy loops. The resulting code … Read more
First, copying into an array that is too small: C has no protection for going past array bounds, so if there is nothing sensitive at dst1[5..9], then you get lucky, and the copy goes into memory that you don’t rightfully own, but it doesn’t crash either. However, that memory is not safe, because it has … Read more
C does not and never has had a native string type. By convention, the language uses arrays of char terminated with a null char, i.e., with ‘\0′. Functions and macros in the language’s standard libraries provide support for the null-terminated character arrays, e.g., strlen iterates over an array of char until it encounters a ‘\0’ … Read more
Your typedef defines Truck as a struct struck *, i.e. a pointer. So it’s size will be 4 or 8 depending on the architecture and not the size of the struct Use sizeof(*Truck) to get the actual size of the struct. You also need to allocate memory for the characters. The easiest way would be … Read more
strcpy is a unsafe function. When you try to copy a string using strcpy() to a buffer which is not large enough to contain it, it will cause a buffer overflow. strcpy_s() is a security enhanced version of strcpy(). With strcpy_s you can specify the size of the destination buffer to avoid buffer overflows during … Read more
strcpy(ptr2, ptr1) is equivalent to while(*ptr2++ = *ptr1++) where as strdup is equivalent to ptr2 = malloc(strlen(ptr1)+1); strcpy(ptr2,ptr1); (memcpy version might be more efficient) So if you want the string which you have copied to be used in another function (as it is created in heap section) you can use strdup, else strcpy is enough.
as Evan pointed out, it is possible to do something like char* s = strcpy(malloc(10), “test”); e.g. assign malloc()ed memory a value, without using helper variable. (this example isn’t the best one, it will crash on out of memory conditions, but the idea is obvious)
Arrays in C are non-assignable and non-copy-initializable. That’s just how arrays are in C. Historically, in value context (on the RHS of assignment) arrays decay to pointers, which is what formally prevents assignment and copy-initialization. This applies to all arrays, not only to char arrays. C language inherits this arrays behavior from its predecessors – … Read more
The local variables have a lifetime which extends only inside the block in which it is defined. The moment the control goes outside the block in which the local variable is defined, the storage for the variable is no more allocated (not guaranteed). Therefore, using the memory address of the variable outside the lifetime area … Read more
The strncpy() function was designed with a very particular problem in mind: manipulating strings stored in the manner of original UNIX directory entries. These used a short fixed-sized array (14 bytes), and a nul-terminator was only used if the filename was shorter than the array. That’s what’s behind the two oddities of strncpy(): It doesn’t … Read more