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

int main(void)
{
  FILE *fp;
  long ft;
  char buf[128], *str = "ewc"; /* 検索する文字列 */
  int i;
  
  if ((fp = fopen("name.dat", "r")) == NULL) exit(1);

  while (1) {
    fgets(buf, 128, fp);
    if (feof(fp)) goto end;
    ft = ftell(fp);
    if (strstr(buf, str)) break;
  }

  fseek(fp, ft, SEEK_SET);
  
  while (1) {
    if (fseek(fp, --ft, SEEK_SET)) goto end;
    i = fgetc(fp);
    if (i == '\n') break;
  }

  fseek(fp, --ft, SEEK_SET);

  while (1) {
    if (fseek(fp, --ft, SEEK_SET)) goto end;
    i = fgetc(fp);
    if (i == '\n') break;
  }

  fseek(fp, --ft, SEEK_SET);

  while (1) {
    if (fseek(fp, --ft, SEEK_SET)) {
      fseek(fp, ++ft, SEEK_SET);
      break;
    }
    i = fgetc(fp);
    if (i == '\n') break;
  }
  
  fgets(buf, 128, fp);
  printf("一行前の行 = %s", buf);
  
end:  
  return 0;
}

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

int
main(int argc, char *argv[])
{
    char buf[2][BUFSIZ] = { {'\0', }, };
    int i;
    int ret = 1;

    if (argc != 2) goto end;

    for (i = 0; NULL != fgets(buf[i], sizeof buf[i], stdin); i ^= 1)
        if (NULL != strstr(buf[i], argv[1])) {
            int j = i ^ 1;
            printf("%s", buf[j]);
        }

    ret = 0;
end:
    return ret;
}