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Why does everyone say not to use scanf? What should I use instead?
Why does everyone say not to use scanf? What should I use instead? scanf has a number of problems, its %s format has the same problem that gets() has --it's hard to guarantee that the receiving buffer won't overflow. More generally, scanf is designed for relatively structured, formatted input (its n... 2015-10-21, 1713👍, 0💬

How can I add N days to a date? How can I find the difference between two dates?
How can I add N days to a date? How can I find the difference between two dates? The ANSI/ISO Standard C mktime and difftime functions provide some (limited) support for both problems. mktime accepts non-normalized dates, so it is straightforward to take a filled-in struct tm, add or subtract from t... 2015-08-05, 1712👍, 0💬

How can I automatically locate a programs configuration files in the same directory as the executable?
How can I automatically locate a programs configuration files in the same directory as the executable? It's hard, in general; Even if you can figure out a workable way to do it, you might want to consider making the program's auxiliary (library) directory configurable, perhaps with an environment va... 2015-03-13, 1712👍, 0💬

Why is the macro giving me the warning
Why is the macro #define TRACE(n) printf("TRACE: %d\n", n) giving me the warning ``macro replacement within a string literal''? It seems to be expanding TRACE(count); as printf("TRACE: %d\count", count); Some pre-ANSI compilers/preprocessors interpreted macro definitions like #define TRACE(var, fmt)... 2016-01-25, 1710👍, 0💬

Was 2000 a leap year?
Was 2000 a leap year? Q: Is (year % 4 == 0) an accurate test for leap years? (Was 2000 a leap year?) A: No, it's not accurate (and yes, 2000 was a leap year). The actual rules for the present Gregorian calendar are that leap years occur every four years, but not every 100 years, except that they do ... 2015-01-05, 1707👍, 0💬

I have an old macro that doesn't seem to work any more....
I have an old macro #define CTRL(c) ('c' &amp; 037) that doesn't seem to work any more. The intended use of this macro is in code like tchars.t_eofc = CTRL(D); which is expected to expand to tchars.t_eofc = ('D' &amp; 037); based on the assumption that the actual value of the parameter c wil... 2016-01-25, 1706👍, 0💬

What's the difference between...?
What's the difference between #include &lt;> and #include "" ? The syntax is typically used with Standard or system-supplied headers, while "" is typically used for a program's own header files. 2016-02-16, 1704👍, 0💬

Is if(p), where p is a pointer, a valid and portable test?
Is if(p), where p is a pointer, a valid and portable test? It is always valid. When C requires the Boolean value of an expression, a false value is inferred when the expression compares equal to zero, and a true value otherwise. That is, whenever one writes if(expr) where ``expr'' is any expression ... 2016-02-29, 1702👍, 0💬

Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0?
Should I use symbolic names like TRUE and FALSE for Boolean constants, or plain 1 and 0? It's your choice. Preprocessor macros like TRUE and FALSE (and, of course, NULL) are used for code readability, not because the underlying values might ever change. It's a matter of style, not correctness, wheth... 2015-05-11, 1702👍, 0💬

People keep saying that the behavior of ...
People keep saying that the behavior of i = i++ is undefined, but I just tried it on an ANSI-conforming compiler, and got the results I expected. A compiler may do anything it likes when faced with undefined behavior (and, within limits, with implementation-defined and unspecified behavior), includi... 2015-11-18, 1700👍, 0💬

How can I read a directory in a C program?
How can I read a directory in a C program? See if you can use the opendir and readdir functions, which are part of the POSIX standard and are available on most Unix variants. Implementations also exist for MS-DOS, VMS, and other systems. (MS-DOS also has FINDFIRST and FINDNEXT routines which do esse... 2015-04-01, 1700👍, 0💬

I thought that using large model meant that I could use more than 64K of data!
What does the error message ``DGROUP data allocation exceeds 64K'' mean, and what can I do about it? I thought that using large model meant that I could use more than 64K of data! Even in large memory models, MS-DOS compilers apparently toss certain data (strings, some initialized global or static v... 2015-03-20, 1698👍, 0💬

Why is p turning out const, instead of the characters pointed to?
I've got the declarations typedef char *charp; const charp p; Why is p turning out const, instead of the characters pointed to? typedef substitutions are not purely textual.In the declaration const charp p; p is const for the same reason that const int i declares i as const. The typedef'ed declarati... 2016-01-04, 1697👍, 0💬

What are near and far pointers?
What are near and far pointers? These days, they're pretty much obsolete; they're definitely system-specific. They had to do with 16-bit programming under MS-DOS and perhaps some early versions of Windows. If you really need to know, see a DOS- or Windows-specific programming reference. If you're us... 2015-03-02, 1697👍, 0💬

Is exit(status) truly equivalent to returning the same status from main?
Is exit(status) truly equivalent to returning the same status from main? Yes and no. The Standard says that a return from the initial call to main is equivalent to calling exit. However, a return from main cannot be expected to work if data local to main might be needed during cleanup; A few very ol... 2015-03-09, 1696👍, 0💬

How can f be used for both float and double arguments in printf? Aren't they different types?
How can f be used for both float and double arguments in printf? Aren't they different types? In the variable-length part of a variable-length argument list, the ``default argument promotions'' apply: types char and short int are promoted to int, and float is promoted to double. (These are the same ... 2015-06-17, 1695👍, 0💬

What is alloca and why is its use discouraged?
What is alloca and why is its use discouraged? alloca allocates memory which is automatically freed when the function which called alloca returns. That is, memory allocated with alloca is local to a particular function's ``stack frame'' or context. alloca cannot be written portably, and is difficult... 2016-03-14, 1694👍, 0💬

How can I read in an object file and jump to locations in it?
How can I read in an object file and jump to locations in it? You want a dynamic linker or loader. It may be possible to malloc some space and read in object files, but you have to know an awful lot about object file formats, relocation, etc., and this approach can't work if code and data reside in ... 2015-03-09, 1693👍, 0💬

When I read numbers from the keyboard with scanf ...
When I read numbers from the keyboard with scanf and a "%d\n" format, like this: int n; scanf("%d\n", &amp;n); printf("you typed %d\n", n); it seems to hang until I type one extra line of input. Perhaps surprisingly, \n in a scanf format string does not mean to expect a newline, but rather to re... 2015-10-23, 1689👍, 0💬

This program runs perfectly on one machine ...
This program runs perfectly on one machine, but I get weird results on another. Stranger still, adding or removing a debugging printout changes the symptoms... Lots of things could be going wrong; here are a few of the more common things to check: * uninitialized local variables integer overflow, es... 2015-05-27, 1689👍, 0💬

How can I generate floating-point random numbers?
How can I generate floating-point random numbers? drand48 is a Unix System V routine which returns floating point random numbers (presumably with 48 bits of precision) in the half-open interval [0, 1). (Its companion seed routine is srand48; neither is in the C Standard.) It's easy to write a low-pr... 2015-07-22, 1688👍, 0💬

How can I ensure that integer arithmetic doesnt overflow?
How can I ensure that integer arithmetic doesnt overflow? The usual approach is to test the operands against the limits in the header file &lt;limits.h> before doing the operation. For example, here is a ``careful'' addition function: int chkadd(int a, int b) { if(INT_MAX - b &lt; a) { fputs... 2015-03-04, 1688👍, 0💬

Why cant I perform arithmetic on a void pointer?
Why cant I perform arithmetic on a void pointer? The compiler doesn't know the size of the pointed-to objects. (Remember that pointer arithmetic is always in terms of the pointed-to size; Therefore, arithmetic on void *'s is disallowed (though some compilers allow it as an extension). Before perform... 2015-12-07, 1686👍, 0💬

Why do some versions of toupper act strangely if given an upper-case letter?
Why do some versions of toupper act strangely if given an upper-case letter? Why does some code call islower before toupper? In earlier times, toupper was a function-like preprocessor macro and was defined to work only on lower-case letters; it misbehaved if applied to digits, punctuation, or letter... 2015-08-17, 1685👍, 0💬

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