please help! adding to strings

This is a discussion on please help! adding to strings within the C Programming forums, part of the General Programming Boards category; I am trying to write to files called something that I give in my command-line. For example I call "a.out ...

  1. #1
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    Sep 2009
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    16

    please help! adding to strings

    I am trying to write to files called something that I give in my command-line. For example I call "a.out blahblah.c16", and then I want to create two new strings "blahblah.o" and "blahblah.syms" and then write to them. I've tried strcat, and doing it character by character, but nothing seems to work.

    This is what I'm working with so far:
    Code:
    	char * name = malloc(sizeof(strlen(argv[1])));
    	strncpy(name, argv[1], s1);
    	printf("name is '%s'\n", name);
            char o[MAXWORDLEN]; //max is 20
    	char syms[MAXWORDLEN];
    
    	puto(o, name);
    	putsyms(syms, name);
    	printf("o is '%s'\n", o);
    	printf("syms is '%s'\n", syms);
    
    	input = fopen(argv[1], "r");
    	output = fopen(syms, "w");
    	output2 = fopen(o, "w");
    here are the methods
    Code:
    int puto(char *str, char *name) {
    	int i = 0;
    	char c = *name;
    	char * name2 = name;
    	while ( ((c>=48 && c <=122) || c == 46) && c!='\0') {
    		str[i] = c;
    		name++;
    		c = *name;
    		i++;
    	}
    	str[i++] = '.';
    	str[i++] = 'o';
    	str[i] = '\0';
    	name = name2;
    	return 0;
    }
    
    int putsyms(char *str, char *name) {
    	int i = 0;
    	char c = *name;
    		while (c != '\0') {
    			str[i] = c;
    			name++;
    			c = *name;
    			i++;
    		}
    		str[i++] = '.';
    		str[i++] = 's';
    		str[i++] = 'y';
    		str[i++] = 'm';
    		str[i++] = 's';
    		str[i] = '\0';
    		return 0;
    }

    >a.out llo.small.int.c16
    name is 'llo.small.int'
    o is ''
    syms is 'llo.small.int.syms'
    FINISHED
    HEX IS 8302
    Segmentation fault (core dumped)

    when I run it in eclipse, it writes to the files fine, but now I'm using a linux server and that doesn't work. Thanks in advance.

  2. #2
    Guest Sebastiani's Avatar
    Join Date
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    Location
    Waterloo, Texas
    Posts
    5,708
    >> strlen(argv[1])

    Good start there, except you forgot to account for the null terminator.

    >> sizeof(strlen(argv[1]))

    strlen returns an int, and sizeof(int) isn't what you want.

    >> strncpy(name, argv[1], s1);

    Not sure what 's1' is, but a better approach would be to store the amount that you passed to malloc somewhere and usee that value instead. Also, not applicable here, but just keep in mind that strncpy doesn't guarantee a null terminator. You might create a wrapper function to make sure that gets done...

    Just a suggestion:

    Code:
    
    int puto(char *str, char *name) {
        int i = 0;
        char c;
        while ((c = name[i]) != '\0' && (c>=48 && c <=122)) {
            str[i++] = c;
        }
        str[i++] = '.';
        str[i++] = 'o';
        str[i] = '\0';
        return 0;
    }
    Also, it would be a better practice to pass a maximum length to the functions to prevent possible overflows.

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