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Questions tagged [c99]

This tag is for questions regarding the International Standard ISO 9899:1999, aka "C99", with technical corrigenda, and for questions about code written in C99 (as opposed to K&R C, C89 or later C Standard revisions like the 2011 revision C11).

This tag is for questions regarding the International Standard ISO 9899:1999 , aka "C99", with technical corrigenda, and for questions about code written in C99 (as opposed to K&R C, C89 or later C Standard revisions like the 2011 revision C11).

Always use the tag for all your C questions, then complement it with the tags for questions that are specific to this version of the standard.

1900 questions
271
votes
6 answers

What is the behavior of integer division?

For example, int result; result = 125/100; or result = 43/100; Will result always be the floor of the division? What is the defined behavior?
T.T.T.
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232
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3 answers

Realistic usage of the C99 'restrict' keyword?

I was browsing through some documentation and questions/answers and saw it mentioned. I read a brief description, stating that it would be basically a promise from the programmer that the pointer won't be used to point somewhere else. Can anyone…
user90052
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172
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4 answers

bool to int conversion

How portable is this conversion. Can I be sure that both assertions pass? int x = 4<5; assert(x==1); x = 4>5; assert(x==0); Don't ask why. I know that it is ugly. Thank you.
pic11
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170
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12 answers

Standard alternative to GCC's ##__VA_ARGS__ trick?

There is a well-known problem with empty args for variadic macros in C99. example: #define FOO(...) printf(__VA_ARGS__) #define BAR(fmt, ...) printf(fmt, __VA_ARGS__) FOO("this works fine"); BAR("this breaks!"); The use of BAR() above is…
jwd
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169
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4 answers

What does dot (.) mean in a struct initializer?

static struct fuse_oprations hello_oper = { .getattr = hello_getattr, .readdir = hello_readdir, .open = hello_open, .read = hello_read, }; I don't understand this C syntax well. I can't even search because I don't know the syntax's…
Benjamin
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161
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5 answers

What is the difference between C, C99, ANSI C and GNU C?

I have started programming practice on codechef and have been confused by the difference between C and C99. What does C mean here? Is it C89? Check the languages at the bottom of this submit. It contains both C and C99. I found on the internet…
Aseem Bansal
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156
votes
9 answers

Printf width specifier to maintain precision of floating-point value

Is there a printf width specifier which can be applied to a floating point specifier that would automatically format the output to the necessary number of significant digits such that when scanning the string back in, the original floating point…
Vilhelm Gray
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150
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5 answers

Why does C++11 not support designated initializer lists as C99?

Consider: struct Person { int height; int weight; int age; }; int main() { Person p { .age = 18 }; } The code above is legal in C99, but not legal in C++11. What was the c++11 standard committee's rationale for excluding support…
xmllmx
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135
votes
5 answers

Can't understand this way to calculate the square of a number

I have found a function that calculates square of a number: int p(int n) { int a[n]; //works on C99 and above return (&a)[n] - a; } It returns value of n2. Question is, how does it do that? After a little testing, I found that between…
Emanuel
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131
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3 answers

How does the below program output `C89` when compiled in C89 mode and `C99` when compiled in C99 mode?

I've found this C program from the web: #include int main(){ printf("C%d\n",(int)(90-(-4.5//**/ -4.5))); return 0; } The interesting thing with this program is that when it is compiled and run in C89 mode, it prints C89 and…
Spikatrix
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118
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3 answers

Is "inline" without "static" or "extern" ever useful in C99?

When I try to build this code inline void f() {} int main() { f(); } using the command line gcc -std=c99 -o a a.c I get a linker error (undefined reference to f). The error vanishes if I use static inline or extern inline instead of just…
Sven Marnach
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118
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7 answers

C99 stdint.h header and MS Visual Studio

To my amazement I just discovered that the C99 stdint.h is missing from MS Visual Studio 2003 upwards. I'm sure they have their reasons, but does anyone know where I can download a copy? Without this header I have no definitions for useful types…
Rob
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111
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3 answers

Are there machines, where sizeof(char) != 1, or at least CHAR_BIT > 8?

Are there machines (or compilers), where sizeof(char) != 1? Does C99 standard says that sizeof(char) on standard compliance implementation MUST be exactly 1? If it does, please, give me section number and citation. Update: If I have a machine (CPU),…
osgx
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103
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12 answers

Visual Studio support for new C / C++ standards?

I keep reading about C99 and C++11 and all these totally sweet things that are getting added to the language standard that might be nice to use someday. However, we currently languish in the land of writing C++ in Visual Studio. Will any of the new…
Colen
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98
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2 answers

C99 boolean data type?

What's the C99 boolean data type and how to use it?
eonil
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