c-preprocessor

#define N 10; int main() { int x; for (int i=0; i<N; i++) x = i; return 0; } Result of compiling this in g++: test-define.cpp: In function ‘int main()’: test-define.cpp:7:22: error: expected primary-expression before ‘;’ token test-define.cpp:7:22: error: expected ‘)’ before ‘;’ token test-define.cpp:7:24: error: name lookup of ‘i’ changed for ISO ‘for’ scoping [-fpermissive] test-define.cpp:7:24: note: (if you use ‘-fpermissive’ G++ will accept your code) test-define.cpp:7:27: error: expected ‘;’ before ‘)’ token But it compiles fine when I change line 7 to for (int i=0; i<10; i++) . Why is

I came across this example of an assertion and was wondering what the # is for: #define ASSERT( x ) if ( !( x ) ) { \ int *p = NULL; \ DBGPRINTF("Assert failed: [%s]\r\n Halting.", #x); \ *p=1; \ } It is the "stringize" preprocessing operator. It takes the tokens passed as the argument to the macro parameter x and turns them into a string literal. #define ASSERT(x) #x ASSERT(a b c d) // is replaced by "a b c d" #x is the stringification directive #define Stringify(x) #x means Stringify(abc) will be substituted with "abc" as in #define initVarWithItsOwnName(x) const char* p = #x int main() {

Using this option I receive files after preprocessing. There are many lines like: # 91 "/usr/include/stdint.h" 3 4 What do the numbers mean? First I thought that #91 is the number of line where file is included, but that is not it. And about 3 4 I have no idea at all. According to the official documentation , the line is of the format: # linenum filename flags The linenum specifies that the following line originated in filename at that line number. Then there are four flags: 1 - Start of a new file 2 - Returning to a file 3 - System header file 4 - Treat as being wrapped in extern "C" So let's

After reading about VA_NARG I tried to implement function overloading depending on number of arguments in C using macros. Now the problem is: void hello1(char *s) { ... } void hello2(char *s, char *t) { ... } // PP_NARG(...) macro returns number of arguments :ref to link above // does not work #define hello(...) hello ## PP_NARG(__VA_ARGS__) int main(void) { hello("hi"); // call hello1("hi"); hello("foo","bar"); // call hello2("foo","bar"); return 0; } I've read this from C-faq. But still could not get it to work... Jens Gustedt This is because of the evaluation rules for macros. You would

PROBLEM I need a way to generate unique values using a preprocessor directive. The aim is that each time the macro is called, it will have a unique integral identifier. But it should retain it's value across files. Kind of like a preprocessor counter for the number of times a call is made to the function. FURTHER INFO The macro I am using is: #define LOG_MSG(a) log_msg(?) 'a' is a string that the user wants to print. log_msg is a custom function used to print a message on the UART The '?' if the part I need help with. This macro would be defined at a single place only. During the preprocessing

This is really odd: : josh@josh; wget ftp://ftp.ruby-lang.org/pub/ruby/1.8/ruby-1.8.7.tar.bz2 : josh@josh; tar xvjf ruby-1.8.7.tar.bz2 : josh@josh; cd ruby-1.8.7/ : josh@josh; CFLAGS='-O0 -g -Wall' ./configure --disable-pthread : josh@josh; make gcc -O0 -g -Wall -DRUBY_EXPORT -D_GNU_SOURCE=1 -I. -I. -c array.c [...] gcc -O0 -g -Wall -DRUBY_EXPORT -D_GNU_SOURCE=1 -I. -I. -c math.c math.c: In function ‘domain_check’: math.c:37: error: missing binary operator before token "(" make: *** [math.o] Error 1 Sure enough, math.c cannot be compiled: : josh@josh; gcc -O0 -g -Wall -DRUBY_EXPORT -D_GNU

Today I came across some C++ code that contains an #ifdef clause like this: #ifdef DISABLE_UNTIL OTHER_CODE_IS_READY foo(); #endif Note the space between "DISABLE_UNTIL" and "OTHER_CODE_IS_READY". Essentially there are two tokens specified in the #ifdef line. My question is, is this legal C++ code? (g++ compiles it without any errors, and it apparently just ignores the second token). And if it is legal, should the second token have any effect? [C++11 16.1] , [C++11 16.5] and, incidentally, [C99 6.10.1/4] all say that this is invalid. if-group : # if constant-expression new-line group opt #

I have a number of very long arrays. No run-time sort is possible. It is also time consuming to sort them manually. Moreover, new elements can be added in any order later, so I would like to sort them by value using C preprocessor or maybe there is any compilers flag (GCC)? For example: sometype S[] = { {somevals, "BOB", someothervals}, {somevals, "ALICE", someothervals}, {somevals, "TIM", someothervals}, } must be sorted so: sometype S[] = { {somevals, "ALICE", someothervals}, {somevals, "BOB", someothervals}, {somevals, "TIM", someothervals}, } SOLVED Ok, here is my solution: Manually copy

I have a table that defines symbols appearance on a 5x7 dot display. Something like: extern UINT8 symbols[][5] = { {0x0,0x0,0x0,0x0,0x0}, {0x0,0x0,0x5F,0x0,0x0}, {0x0,0x7,0x0,0x7,0x0}, {0x14,0x7F,0x14,0x7F,0x14}, // etc. The leading part of the table matches ASCII table, followed by a set of special symbols, e.g. an arrow, or a check-mark. To reference those I have a list of macros: #define SYMBOL_LEFT_ARROW 120 // 120 is the entry in the table #define SYMBOL_RIGHT_ARROW (SYMBOL_LEFT_ARROW+1) #define SYMBOL_UP_ARROW (SYMBOL_RIGHT_ARROW+1) Now I need to say something like (won't compile): const