macro function

This is a discussion on macro function within the C Programming forums, part of the General Programming Boards category; Hello everyone, I am stuck and confused about macros. I need to define a macro that returns the HOME dir ...

  1. #1
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    macro function

    Hello everyone,
    I am stuck and confused about macros. I need to define a macro that returns the HOME dir of user. This is what I have so far:
    Code:
    #define GLADE_FILE { \
        char *homeDir = getenv("HOME"); \
        char *tempi = "/hello.glade"; \
        strcat(homeDir, tempi); \ 
        printf("%s", homeDir); \
    }
    as you can see it does not work. If I try to put it into a regular function and try to pass homeDir with return(homeDir)
    I get
    home-dir.c:19: warning: return makes integer from pointer without a cast
    Any help would be great,
    Thanks in advance.
    Brad

  2. #2
    Deathray Engineer MacGyver's Avatar
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    You can't just strcat them together like that. I doubt getenv() will return enough of a buffer to guarentee that it will be safe.

    In reality, you should make this into a function imo.

  3. #3
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    Quote Originally Posted by bradleyd View Post
    Hello everyone,
    I am stuck and confused about macros. I need to define a macro that returns the HOME dir of user. This is what I have so far:
    Code:
    #define GLADE_FILE { \
        char *homeDir = getenv("HOME"); \
        char *tempi = "/hello.glade"; \
        strcat(homeDir, tempi); \ 
        printf("%s", homeDir); \
    }
    as you can see it does not work. If I try to put it into a regular function and try to pass homeDir with return(homeDir)
    I get
    Any help would be great,
    Thanks in advance.
    Brad
    Code:
    #define PATHLEN 256 
    
     char mypath[PATHLEN] = { '\0' };
     char *homeDir = getenv("HOME");
     strncpy(mypath, homeDir, PATHLEN);
     strncat(mypath, "/hello.glade", PATHLEN - strlen(mypath));
     printf("%s", mypath);
    Last edited by Brian; 05-20-2007 at 09:26 PM. Reason: '\0' not 0

  4. #4
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    I tried to put it into a function then call the function but I get that error. Here is the function:
    Code:
    char hd(void)
    {
    	char *homeDir = getenv("HOME");
        char *temp = "/hello.glade";
        strcat(homeDir, temp);
        return(homeDir);
    }
    if I substitute return(homeDir) with printf("%s",homeDir);
    it works fine.

  5. #5
    Deathray Engineer MacGyver's Avatar
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    If you just want to print it without any error checking, then you could do something like this:

    Code:
    #define printglade() printf("%s/hello.glade",getenv("HOME"))
    Since getenv() can return NULL, this is probably not a good idea.

    If you need to return a string:

    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <string.h>
    
    char *getGlade(void);
    
    int main(void)
    {
    	char *szGlade = getGlade();
    	
    	if(szGlade)
    	{
    		printf("Glade directory: <%s>\n",szGlade);
    		free(szGlade);
    	}
    	else perror("Unable to retrieve Glade directory.");
    	
    	return 0;
    }
    
    char *getGlade(void)
    {
    	char *homeDir,*temp = "/hello.glade",*szReturn = NULL;
    	
    	homeDir = getenv("HOME");
    	if(homeDir)
    	{
    		szReturn = malloc(strlen(homeDir) + strlen(temp) + 1);
    		if(szReturn)
    		{
    			strcpy(szReturn,homeDir);
    			strcat(szReturn,temp);
    		}
    	}
    	return szReturn;
    }

  6. #6
    Woof, woof! zacs7's Avatar
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    Quote Originally Posted by bradleyd View Post
    I tried to put it into a function then call the function but I get that error. Here is the function:
    Code:
    char hd(void)
    {
    	char *homeDir = getenv("HOME");
        char *temp = "/hello.glade";
        strcat(homeDir, temp);
        return(homeDir);
    }
    if I substitute return(homeDir) with printf("&#37;s",homeDir);
    it works fine.
    Your supposed to return a char pointer (char *) not a char, see MacGyver's post.

  7. #7
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    Thanks that worked, I kinda foggy on char *GetHome vs. char GetHome. If you want to return any string from a function do you always have use a pointer in declaring the function?
    when you want to return a int you just int SomeNumber(void).
    Just having trouble grasping that.
    Thanks,
    Brad

  8. #8
    Deathray Engineer MacGyver's Avatar
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    A string is a set of chars that are sequential in memory, ending with a final '\0' char. One way of representing such a data type can be done using a char array. A char array, down deep under the hood, is represented simply by a pointer to the first element of the array. This means to return a string, you have to return a char *. If you return a char, you only return one character.

  9. #9
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    ok that makes sense, thanks MacGyver.
    Pointers seem to be my weak point in C.

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