Đọc và ghi CSV

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

/* Ghi mot truong CSV, tu bao dau nhay khi can. */
int csv_ghi_truong(FILE *f, const char *s) {
    int can_nhay = (*s == '\0')
                   || strpbrk(s, ",\"\n\r") != NULL
                   || s[0] == ' '
                   || s[strlen(s) - 1] == ' ';

    if (!can_nhay) return fputs(s, f) == EOF ? -1 : 0;

    if (fputc('"', f) == EOF) return -1;

    for (const char *p = s; *p; ++p) {
        if (*p == '"' && fputc('"', f) == EOF) return -1;   /* nhan doi */
        if (fputc(*p, f) == EOF) return -1;
    }

    return fputc('"', f) == EOF ? -1 : 0;
}

/* Ghi ca mot dong */
int csv_ghi_dong(FILE *f, const char *truong[], size_t n) {
    for (size_t i = 0; i < n; ++i) {
        if (i > 0 && fputc(',', f) == EOF)  return -1;
        if (csv_ghi_truong(f, truong[i]) != 0) return -1;
    }

    return fputs("\r\n", f) == EOF ? -1 : 0;
}

#include <stddef.h>

/* Tach mot dong CSV TAI CHO. Tra ve so truong tim duoc.
   ra[i] tro vao chinh bo dem dong, da bo dau nhay
   va da giai thoat dau nhay kep.

   Chuoi vao phai GHI DUOC. */
size_t csv_tach(char *dong, char *ra[], size_t toi_da) {
    size_t n = 0;
    char  *p = dong;

    while (n < toi_da) {
        char *ghi = p;             /* con tro ghi, luon chay sau hoac bang p */

        ra[n++] = ghi;

        if (*p == '"') {                        /* truong co dau nhay */
            ++p;

            for (;;) {
                if (*p == '\0') break;          /* dau nhay khong dong */

                if (*p == '"') {
                    if (p[1] == '"') {          /* hai nhay lien: mot nhay that */
                        *ghi++ = '"';
                        p += 2;

                        continue;
                    }

                    ++p;                        /* dau nhay dong */

                    break;
                }

                *ghi++ = *p++;
            }
        } else {                                /* truong tran */
            while (*p != ',' && *p != '\0' && *p != '\n' && *p != '\r')
                *ghi++ = *p++;
        }

        int het = (*p != ',');

        if (*p == ',') ++p;

        *ghi = '\0';                            /* ket thuc truong vua ghi */

        if (het) break;
    }

    return n;
}

/* Doc dong dau, tim vi tri tung cot theo TEN chu khong theo THU TU */
int doc_tieu_de(char *dong, int *vt_mssv, int *vt_ten, int *vt_diem) {
    char  *cot[32];
    size_t n = csv_tach(dong, cot, 32);

    *vt_mssv = *vt_ten = *vt_diem = -1;

    for (size_t i = 0; i < n; ++i) {
        if      (strcmp(cot[i], "mssv")   == 0) *vt_mssv = (int)i;
        else if (strcmp(cot[i], "ho_ten") == 0) *vt_ten  = (int)i;
        else if (strcmp(cot[i], "diem")   == 0) *vt_diem = (int)i;
    }

    if (*vt_mssv < 0 || *vt_ten < 0 || *vt_diem < 0) {
        fprintf(stderr, "Thieu cot bat buoc trong dong tieu de\n");

        return -1;
    }

    return 0;
}

/* Nho cach nay, tep co them cot moi hay doi thu tu cot
   van doc duoc, mien la ba cot bat buoc con do. */

/* Excel ghi tep UTF-8 kem BOM: ba byte EF BB BF o dau tep.
   Neu khong bo di thi ten cot dau tien thanh "\xEF\xBB\xBFmssv"
   va moi phep strcmp deu that bai. */

static void bo_bom(char *dong) {
    unsigned char *b = (unsigned char *)dong;

    if (b[0] == 0xEF && b[1] == 0xBB && b[2] == 0xBF)
        memmove(dong, dong + 3, strlen(dong + 3) + 1);
}