Iterate through input char argument in C?

Question

I am trying to iterate through an input argument in C which I'm storing in a pointer to char like this: const char *page = argv[1];

Now the argument is going to be a http address so it might look something like this:

http://host:port/folder1/folder2/file.jpg

And what I want is: to parse this string and separate it to substrings

char host = "host"; 
char port = "port"; 
char path = "/folder1/folder2/file.jpg";
char file = "file.jpg";

So I thought a simple for loop counting the number of slashes for example might do the trick.

int slash_cnt = 0;
int i = 0;

for (i = 0, page[i] != '\0', i++)
{ 
    if (strcmp(&page[i], "/")) 
    { 
        slash_cnt++; 
    }
}

But this isn't working.

If anybody could help me out here or even suggest a better way to parse the http address specified in the input and separate it accordingly, I'd be very grateful!

Well I just tried writing a custom parser and as you can see it's not working so, that's why I'm asking the question : ) — Daeto
– Daeto, Commented Mar 12, 2017 at 12:57
strcmp() compares strings, not individual characters or parts of strings. RTFM. — Peter
– Peter, Commented Mar 12, 2017 at 12:57
well if (strcmp(&page[i], "/")) can be simplified to if (page[i] == '/')). And can you please make it a little clearer what you want this parser to do? If you wanted to clean things up you could have an array of char* and access them through an enum. Anyway, the best thing to do, is to call strcpy on the pointers current pos - the last pos where you found a slash ( or the begging of the string ). — George
– George, Commented Mar 12, 2017 at 12:57
@George - strcmp(&page[i], "/") is not equivalent to page[i] == '/'. — Peter
– Peter, Commented Mar 12, 2017 at 12:59

xing · Accepted Answer · 2017-03-12 16:45:18Z

strstr could be used to search for the strings //, / and : that separate the sections of interest. strrchr could be used to find the trailing / that precedes the filename.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int main()
{
    char *page = "http://host:port/folder1/folder2/file.jpg";
    char *slashes = "//";
    char *slash = "/";
    char *colon = ":";
    char *start = NULL;
    char *stop = NULL;
    char *host = NULL;
    char *port = NULL;
    char *path = NULL;
    char *file = NULL;
    size_t span = 0;

    if ( ( start = strstr ( page, slashes)) == NULL) {
        fputs ( "could not find \"//\"\n", stderr);
        return 1;
    }
    start += strlen ( slashes);//move pointer so the slashes are excluded
    if ( ( stop = strstr ( start, colon)) == NULL) {
        fputs ( "could not find \":\"\n", stderr);
        return 1;
    }
    span = stop - start;
    if ( ( host = malloc ( span)) == NULL) {
        fputs ( "malloc failed\n", stderr);
        return 1;
    }
    memmove ( host, start, span);
    host[span] = '\0';

    start = stop + strlen ( colon);
    if ( ( stop = strstr ( start, slash)) == NULL) {
        fputs ( "could not find leading \"/\"\n", stderr);
        return 1;
    }
    span = stop - start;
    if ( ( port = malloc ( span)) == NULL) {
        fputs ( "malloc failed\n", stderr);
        return 1;
    }
    memmove ( port, start, span);
    port[span] = '\0';

    span = strlen ( stop) + 1;
    if ( ( path = malloc ( span)) == NULL) {
        fputs ( "malloc failed\n", stderr);
        return 1;
    }
    memmove ( path, stop, span);
    path[span] = '\0';

    if ( ( start = strrchr ( page, slash[0])) == NULL) {
        fputs ( "could not find trailing \"/\"\n", stderr);
        return 1;
    }
    start += strlen ( slash);
    span = strlen ( start) + 1;
    if ( ( file = malloc ( span)) == NULL) {
        fputs ( "malloc failed\n", stderr);
        return 1;
    }
    memmove ( file, start, span);
    file[span] = '\0';

    puts ( host);
    puts ( port);
    puts ( path);
    puts ( file);

    free ( host);
    free ( port);
    free ( path);
    free ( file);

    return 0;
}

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