It is consistent behavior, you’re just thinking about it wrong. 😉 scanf(“%c”, some_char); // reads a character from the key board. scanf(“%d”, some_int); // reads an integer from the key board. So if I do this: printf(“Insert a character: “); scanf(“%c”, &ch); // if I enter ‘f’. Really I entered ‘f’ + ‘\n’ // scanf … Read more
If you read the specification for scanf() carefully, most format specifiers skip leading white space. In Standard C, there are three that do not: %n — how many characters have been processed up to this point %[…] — scan sets %c — read a character. (POSIX adds a fourth, %C, which is equivalent to %lc.) … Read more
printf(“Hello World!”); is IMHO not vulnerable but consider this: const char *str; … printf(str); If str happens to point to a string containing %s format specifiers, your program will exhibit undefined behaviour (mostly a crash), whereas puts(str) will just display the string as is. Example: printf(“%s”); //undefined behaviour (mostly crash) puts(“%s”); // displays “%s\n”
Breakdown of scanf(“%*[^\n]%*c”): %*[^\n] scans everything until a \n, but doesn’t scan in the \n. The asterisk(*) tells it to discard whatever was scanned. %*c scans a single character, which will be the \n left over by %*[^\n] in this case. The asterisk instructs scanf to discard the scanned character. Both %[ and %c are … Read more
There is none. Use a temp object as the size of _Bool is implementation dependent. #include <stdbool.h> #include <stdio.h> bool b; int temp; scanf(“%d”, &temp); b = temp;
MS Visual Studio didn’t support %zu printf specifier before VS2013. Starting from VS2013 (e.g. _MSC_VER >= 1800) %zu is available. As an alternative, for previous versions of Visual Studio if you are printing small values (like number of elements from std containers) you can simply cast to an int and use %d: printf(“count: %d\n”, (int)str.size()); … Read more
Yes: use the z length modifier: size_t size = sizeof(char); printf(“the size is %zu\n”, size); // decimal size_t (“u” for unsigned) printf(“the size is %zx\n”, size); // hex size_t The other length modifiers that are available are hh (for char), h (for short), l (for long), ll (for long long), j (for intmax_t), t (for … Read more
%lu is the correct format for unsigned long. Sounds like there are other issues at play here, such as memory corruption or an uninitialized variable. Perhaps show us a larger picture?
From the latest C11 draft: §7.16.1.1/2 …if type is not compatible with the type of the actual next argument (as promoted according to the default argument promotions), the behavior is undefined, except for the following cases: — one type is a signed integer type, the other type is the corresponding unsigned integer type, and the … Read more
One possible reason: for symmetry with the use of those modifiers in the formatted input functions? I know it wouldn’t be strictly necessary, but maybe there was value seen for that? Although they don’t mention the importance of symmetry for the “h” and “hh” modifiers in the C99 Rationale document, the committee does mention it … Read more