find the cwd of the currently focused window (in order to spawn another command in that cwd) in dwm. not finished yet.

dwm-spawncwd-incomplete.c

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

#define LENGTH(X) (sizeof(X) / sizeof(X[0]))

void getproccwd(const unsigned int pid, char *cwd, const unsigned int size);
void getdesc(const unsigned int pid, int *desc, const unsigned int size);
int descappend(const unsigned int pid, int *desc, const unsigned int size);
int readfile(const char *path, char *ret, const unsigned int size);

int PID = 1;

int main(void)
{
    char cwd[1024];
    getproccwd(PID, cwd, sizeof(cwd));
    printf("%s\n", cwd);
}

void getproccwd(const unsigned int pid, char *cwd, const unsigned int size)
{
    int desc[32] = { -1 };
    getdesc(pid, desc, sizeof(desc));
    for (int i = 0; i < LENGTH(desc) && desc[i] >= 0; i++) {
        char path[32];
        snprintf(path, sizeof(path), "/proc/%u/cwd", desc[i]);
        ssize_t len;
        if ((len = readlink(path, cwd, size - 1)) <= 0)
            continue;
        cwd[len] = '\0';
        if (strncmp(cwd, getenv("HOME"), size) != 0)
            return;
    }
    cwd[0] = '\0';
}

void getdesc(const unsigned int pid, int *desc, const unsigned int size)
{
    char ptrn[64];
    glob_t gl;
    int gl_ret;

    snprintf(ptrn, sizeof(ptrn), "/proc/%u/task/[0-9]*/children", pid);

    gl_ret = glob(ptrn, GLOB_NOSORT, NULL, &gl);
    if (gl_ret == GLOB_NOMATCH || gl_ret == GLOB_ABORTED || gl_ret == GLOB_NOSPACE)
        return;

    for (int i = 0; i < gl.gl_pathc; i++) {
        char pids[128];
        if (!(readfile(gl.gl_pathv[i], pids, sizeof(pids))))
            continue;
        char *state = NULL;
        char *chpidstr = strtok_r(pids, " ", &state);
        for (; chpidstr; chpidstr = strtok_r(NULL, " ", &state)) {
            unsigned int chpid = (unsigned int)strtoul(chpidstr, NULL, 10);
            if (!(descappend(chpid, desc, size))) {
                globfree(&gl);
                return;
            }
            getdesc(chpid, desc, size);
        }
    }
    globfree(&gl);
}

int descappend(const unsigned int pid, int *desc, const unsigned int size)
{
    unsigned int i = 0;
    unsigned int count = size / sizeof(int);
    for (; i < count && desc[i] >= 0; i++);
    if (i >= count)
        return 0;
    desc[i++] = pid;
    if (i < count)
        desc[i] = -1;
    return 1;
}

int readfile(const char *path, char *ret, const unsigned int size)
{
    unsigned int i = 0;
    int c;
    FILE *f;
    if (!(f = fopen(path, "r")))
        return 0;
    while (i < (size / sizeof(char)) - 1 && ((c = fgetc(f)) != EOF))
        ret[i++] = c;
    fclose(f);
    ret[i] = '\0';
    return 1;
}