How to declare the data type for variable arguments? - c

Question

I'm trying to assign data type to world but unable to figure it out.
#include <stdarg.h>
#include <stdio.h>
#define TRACE(arg) TraceDebug arg ;\
void TraceDebug(const char* format, ...);
void TraceDebug(const char* format, ...)
{
char buffer[256];
va_list args;
va_start(args, format);
vprintf(format, args);
va_end(args);
}
int main(void)
{
int a =55;
TRACE((Hello,a));
return 0;
}
Below is the error statement in detail.
main.c: In function 'main':
main.c:28:12: error: 'Hello' undeclared (first use in this function)
TRACE((Hello,a));
^
main.c:13:32: note: in definition of macro 'TRACE'
#define TRACE(arg) TraceDebug arg ;\
^
main.c:28:12: note: each undeclared identifier is reported only once for each function it appears in
TRACE((Hello,a));
^
main.c:13:32: note: in definition of macro 'TRACE'
#define TRACE(arg) TraceDebug arg ;\
^
Is there anyway possible to declare Hello as a variable, after declaring I need to get the address of the variable.
In simple I want to change the below code into a variadic function arguments
for example #define QU(arg1,arg2) as #define QU(arg1,...) since variadic macro is not supported am using variadic functions.
#define TRACE(arg1) QU arg1
#define QU(arg1,arg2) {static const char arg1; \
printf("%p\n",(void*)&arg1);\
printf("%d\n",arg2);}\
int main(void)
{
int aaa =333;
int bbb =444;
TRACE((Hello,aaa));
TRACE((Hello2,bbb));
return 0;
}

Answer 1

1) (title) How to declare the data type for variable arguments?
2) (1st question) I'm trying to assign data type to world but unable to figure it out.
1) The data type for the variadic argument (represented by the ellipses: ... ) is always the type of the variable preceding the ellipses . For this prototype:
int variadicFunc(int a, const char *b, ...);
^^^^^^^^^^ ^^^
type assumes the type const char *
2) From content of your question only, the answer could be to be use a typedef statement:
typedef char World; // a new type 'World' is created
But there are clarifications in the comments:
if i change the string to variable i can reduce the memory size,... (you)
You want to have a variable argument list to pass variables existing in your program that you want to place on a Trace list for debugging
purposes. (is that close?)... (me)
(is that close?) yes, that's the thing am trying to do... Are you always going to pass the same type to this function? Ahh, type will
be like TRACE(("Hello", a,"world")); (you)
It appears you want to enter a variable number of either string literals, or string variables as function arguments, then for those items to be placed into variables, then the addresses of those variables to be stored in a file, for the purpose of saving space.
The following code illustrates how you can pass a variable number of strings (in different forms) into a function, and have the address and content retained into a struct. From this, you should be able to adapt from what I have done here, to something more useful to your needs. Note, I have reserved the first string argument to be used a file location to store addresses.
#define MAX_LEN 200
typedef struct {
unsigned int addr;
char str[MAX_LEN];
} DATA;
int variadicFunc(int argCount, const char *str, ...);
int main(void)
{
char a[] = {"this is a string"};
char b[] = {"another string"};
char c[] = {"yet another string"};
// count non-variable v1 v2 v3 v4
variadicFunc(4, ".\\storage.txt", a, b, "var string", c);
// ^count of variable argument list
return 0;
}
int variadicFunc(int argCount, const char *str, ...)
{
va_list arg;
int i;
char sAddr[10];
DATA *d = calloc(argCount, sizeof(*d));
va_start(arg, str);
FILE *fp = fopen(str, "w");//using first string as filename to populate
if(fp)
{
for(i=0;i<argCount;i++)
{
// retain addresses and content for each string
strcpy(d[i].str, va_arg(arg, const char *));
d[i].addr = (unsigned int)&d[i].str[i];
sprintf(sAddr, "%X\n", d[i].addr);
fputs(sAddr, fp);
}
fclose(fp);
}
return 0;
}