Parsing a string

This is a discussion on Parsing a string within the C Programming forums, part of the General Programming Boards category; Hi! I wrote a function which parses a string like this: "str0\0str1\0.....strN\0" into an array of string like this: arg[0]="str0" ...

  1. #1
    gcc -Wall -pedantic *.c
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    Parsing a string

    Hi! I wrote a function which parses a string like this: "str0\\0str1\\0.....strN\\0"
    into an array of string like this:

    arg[0]="str0"
    arg[1]="str1"
    .
    .
    arg[N]="strN"

    it works fine,... but when the last string (strN) is not followed by "\\0" it doesn't work!

    Code:
    char** get_args(char *args, int lim) {
    	int read=0, i, k=0;
    	char **tmp;printf("Get args riceve: %s\n", args);
    	ec_null( (tmp=(char**)malloc(sizeof(char*)*lim)), 0 )
    	for (i=0; i<=strlen(args); i++) {
    		if (read>lim) return NULL;
    		if ((args[i]=='\\' && (!(args+i+1) ||
    				args[i+1]=='0')) || i==strlen(args)) {
    			ec_null( (tmp[read]=(char*)malloc(sizeof(char)*(i-k+1))), 0);
    			snprintf(tmp[read++], i-k+1, "%s", args+k);
    			k=(++i)+1;
    		}
    	}
    	if (read==lim)
    		return tmp;
    	return NULL;
    }
    The parameter "lim" is an integer that indicates the number of arguments the function has to find, if more or less than lim arguments will be found the function will return NULL to indicate there's an error!
    Thanks!

  2. #2
    spurious conceit MK27's Avatar
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    First off, I presume by
    a string like this: "str0\\0str1\\0.....strN\\0"
    You actually meant a string like this str0\0str1\0strN\0, and that you are trying to match a \ with'\\'.

    There are number of problems in this line:
    Code:
    if ((args[i]=='\\' && (!(args+i+1) ||
    				args[i+1]=='0')) || i==strlen(args)) {
    This part is wrong. Advancing a pointer to point to something undefined does not make it NULL.
    So this part would mean "(if) the last character in args is \", except that it will never be true because of that.
    This part needs brackets to be functional, and it would mean "(if) this is the last character in args".
    C programming resources:
    GNU C Function and Macro Index -- glibc reference manual
    The C Book -- nice online learner guide
    Current ISO draft standard
    CCAN -- new CPAN like open source library repository
    3 (different) GNU debugger tutorials: #1 -- #2 -- #3
    cpwiki -- our wiki on sourceforge

  3. #3
    gcc -Wall -pedantic *.c
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    Yes i meant a string in that way, exactly!
    Thanks for the useful information, i'll change the code tomorrow and i will let you know!

  4. #4
    gcc -Wall -pedantic *.c
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    I changed something in the code, what you said about the undefined value of the pointers is true! But the function assumes that the string args (parameter), is null terminated. Now it's working as i wanted, here there's the new version.

    Code:
    char** get_args(char *args, int lim) {
    	int read=0, i, k=0;
    	char **tmp;
    	ec_null( (tmp=(char**)malloc(sizeof(char*)*lim)), 0 )
    	for (i=0; i<=strlen(args); i++) {
    		if (read>lim) return NULL;
    		if (i<strlen(args)) {
    			if ((args[i]=='\\' && (!(args+i+1) ||
    					args[i+1]=='0'))) {
    				ec_null( (tmp[read]=(char*)malloc(sizeof(char)*(i-k+1))), 0);
    				snprintf(tmp[read++], i-k+1, "%s", args+k);
    				k=(++i)+1;
    			}
    		}
    	}
    	if (read==lim)
    		return tmp;
    	return NULL;
    }
    Your suggestions have been appreciated!
    Cheers!

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