extracting substring from string using pointers in C

Question

I currently am trying to extract a substring within a bufferline. The goal is to parse the string by whitespace and symbols to compile later. The line I'm trying to parse is the first line of my file.

void append(char* s, char c)
{
    int len = strlen(s);
    s[len] = c;
    s[len+1] = '\0';
}

int main(void){    
    char str[] = "program example(input, output);";

    char *f = str;
    char *b = str;

    char token[10];

    if(*f != '\0'){
        while (*f != ' ')
        {
            append(token,*f);
            f++;
        }
        f++;
        printf("%s",token);
        token[9] = '\0';
    }
    return 0;
}

Am I clearing the token string wrong? The code only returns:

program

but it should return

program
example(input,
output);

Tano Fotang · Accepted Answer · 2018-09-23 21:21:11Z

1

There are a few things fundamentally wrong with your code (possibility of buffer overflow in your append() function, etc). I have changed just enough to allow the code to produce the desired result, to my understanding.

int main(void){    
    char str[] = "program example(input, output);";

    char *f = str;

    char *token=(char *)malloc((strlen(str)+1)*sizeof(char));
    char *b = token;

    while(*f != '\0'){
        while (*f && *f != ' ')
        {
            *b++=*f;
            f++;
        }
        if(*f) f++;
        *b=0;
        b=token;
        printf("%s\n",token);
    }
    free(token);
    return 0;
}

$ ./a.out 
program
example(input,
output);

edited Sep 23, 2018 at 21:21

answered Sep 23, 2018 at 21:11

Tano Fotang

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1 Comment

compilerNewbie Over a year ago

Thank you! My goal is to separate the each token. This should get me on the right track now.

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