Simple example of how to parse arguments from a single string, with quote-handling.

parse_args.c

/*
 * Test for parsing command-line arguments from a single string
 *
 * gcc -std=c11 -Wall -Werror -Wextra -pedantic -pedantic-errors parse_args.c -o parse_args
 */
#include <stdio.h> // printf(), fprintf()
#include <string.h> // strlen()
#include <stdbool.h> // bool, true, false
#include <ctype.h> // isspace()

/*-------------------------------------
 * Count the number of arguments in an argument string
-------------------------------------*/
bool _args_from_string(char* const pArgString)
{
    if (!pArgString || pArgString[0] == '\0')
    {
        fprintf(stderr, "Invalid input: %s\n", pArgString);
        return false;
    }
    
    unsigned argc    = 0;
    bool isQuotedS   = false;
    bool isQuotedD   = false;
    bool isEscaped   = false;
    bool wasQuotedD  = false;
    bool wasQuotedS  = false;
    unsigned lastArg = 0;
    unsigned i       = 0;

    // count all arguments in the string    
    do
    {
        const char c = pArgString[i];

        // single quotes embedded in double quotes aren't counted
        // and vice-versa
        if ((c == '\"') && !isEscaped && !isQuotedS)
        {
            isQuotedD = !isQuotedD;
            wasQuotedD = true;
            ++lastArg;
        }

        if ((c == '\'') && !isEscaped && !isQuotedD)
        {
            isQuotedS = !isQuotedS;
            wasQuotedS = true;
            ++lastArg;
        }
        
        const bool wasQuoted   = wasQuotedS || wasQuotedD;
        const bool isQuoted    = isQuotedS || isQuotedD;
        const bool isDelimiter = (!isEscaped && isspace(c)) || c == '\0';
        
        // count arguments which are not separated by an escaped space
        if (isDelimiter && !isQuoted)
        {
            const unsigned length    = i - wasQuoted;
            const char* subStr       = pArgString + lastArg;
            const char temp          = pArgString[length];
            pArgString[length]       = '\0';
            
            printf("Argument found: %s\n", subStr);
            // printf("\tQuoted: %d\n", wasQuoted);
            // printf("\tOffset: %u - %u\n", lastArg, length);
            // printf("\tlength: %zu\n", strlen(subStr));
            
            pArgString[length]      = temp;
            lastArg                 = i;
            isQuotedS = isQuotedD   = false;
            wasQuotedS = wasQuotedD = false;
            
            ++argc;
        }

        // Flip the check for character escapes
        isEscaped = (c == '\\');
    }
    while (pArgString[i++] != '\0');
    
    // printf("%d arguments found in the input string: %s\n\n", argc, pArgString);
    
    return !isQuotedS && !isQuotedD;
}



int main(int argc, char* argv[])
{
    int ret = 0;

    printf("%d Arguments available to parse.\n", argc);
    
    for (int i = 0; i < argc; ++i)
    {
        ret += _args_from_string(argv[i]);
    }
    
    return ret;
}