Parsing command line for execve() error. Plain C

Question

I'm new to C pointers and trying to execute process with command line and obtain its pid. Any of system(), sh(), etc, that use command line doesn't return pid, so I desided to use execve(). But it needs command line to be parsed to string array.

I found some existing solutions, but I could not make any to work. So, I wrote mine own. It works in my test program, but causes segmentation error in real one. Can somebody tell me, where I am wrong? Code is:

void cmdline_to_argv(const char* cmd_line, char*** argv, int* argc){
    int len, i, count, spc;
    char *s,*d;
    /* make a copy to play with */
    char *cmd_line1 = strdup(cmd_line);

    /* count items to deal with and trim multiple spaces */
    d = s = cmd_line1; spc = 1; count = 0; len=strlen(cmd_line1);
    for (i=0; i<len;i++,s++) {
        switch (*s) {
        case ' ':
            if (spc) continue;
            *d++ = '\0'; /* replace spaces with zeroes */
            spc = 1;
            break;
        default:
            if (spc) { count++; spc = 0; }
            *d++ = *s;
        }
    }
    (*d++) = '\0'; /* line termination */
    /* reallocate copy to correct size */
    cmd_line1 = realloc( cmd_line1, d - cmd_line1);
    /* allocate array of poiters */
    *argv = (char**) malloc(sizeof(char*) * (count+1));
    argv[count] = NULL;
    /* scan line again to find all lines starts and register */
    s = cmd_line1;
    for (i=0; i<count; i++) {
        (*argv)[i] = s;
        while (*(s++)) ;
    }
    *argc = count;
}

and there is how I call it:

char **chargv = NULL;
int chargc;

/* parse line to argument array */
cmdline_to_argv(cmdline, &chargv, &chargc);

I think all the trouble here with pointer operations where I allocate array and write to it. How to do it correct?

Answer 1

The question is closed. Solution is found. The tricky pointer declaration syntax solved. Here is the working one.

Thanks to All. :-|

 void cmdline_to_argv(const char* cmd_line, char ***argv, int* argc){
    int i, spc;
    size_t len;
    char *s,*d;
    /* make a copy to play with */
    char *cmd_line1 = strdup(cmd_line);

    /* count items to deal with and trim multiple spaces */
    d = s = cmd_line1; spc = 1; *argc = 0; len=strlen(cmd_line1);
    for (i=0; i<len;i++,s++) {
        switch (*s) {
        case ' ':
            if (spc) continue;
            *d++ = '\0'; /* replace spaces with zeroes */
            spc = 1;
            break;
        default:
            if (spc) { (*argc)++; spc = 0; }
            *d++ = *s;
        }
    }
    (*d++) = '\0'; /* line termination */
    /* calc actual size */
    len = d - cmd_line1;
    /* allocate array of poiters */
    *argv = (char**) malloc(sizeof(char*) * ((*argc)+1) + len);
    (*argv)[*argc] = (char*) NULL;
    d = (char*) &(*argv)[(*argc)+1];
    memmove(d, cmd_line1, len);
    free(cmd_line1);
    cmd_line1 = d;
    /* scan line again to find all lines starts and register */
    for (i=0; i<*argc; i++) {
        (*argv)[i] = d;
        while (*(d++)) ;
    }
}

/* deallocate array and strings */
void free_argv(char ***argv) {
    free(*argv); /* strings laying together at once after pointers array */
}

Answer 2

Have you looked here https://www.kernel.org/doc/man-pages/online/pages/man2/getpid.2.html I believe what you want is getpid() although maybe you are asking something more.