如何輸出到C中的兩個單獨的文件和命令行？

Question

假設我有一個將結果打印到文件的程序。但是我想要將相同的結果打印到另一個文件和命令行中。我試圖創建另一個文件，但我不斷收到錯誤：當對該文件進行錯誤檢查時，「下標值既不是數組也不是指針」。我會如何去做這件事？這是我的節目裏，結果被打印到一個文件：

#include <stdio.h> 
#include <stdlib.h> 
int main(int argc, char *argv[]) 
{ 
    int offset; 
    int ch1, ch2; 
    FILE *fh1, *fh2, *diffone=stdout; 


    if(argc<3) { 
     printf("need two file names\n"); return(1); 
    } 
    if(!(fh1 = fopen(argv[1], "r"))) { 
     printf("cannot open %s\n",argv[1]); return(2); 
    } 
    if(!(fh2 = fopen(argv[2], "r"))) { 
     printf("cannot open %s\n",argv[2]); return(3); 
    } 
    if(argc>3) { 
     if(!(diffone = fopen(argv[3], "w+"))) { 
      printf("cannot open %s\n",argv[3]); return(4); 
     } 
    } 

    while((!feof(fh1)) && (!feof(fh2))) 
    { 
     ch1=ch2='-'; 
     if(!feof(fh1)) ch1 = getc(fh1); 
     if(!feof(fh2)) ch2 = getc(fh2); 
     if(ch1 != ch2) 
      fprintf(diffone,"%c", ch1);//How do I print this to another file and the command line as well? 
     } 


    return 0; 
} 

Answer 1

#include <stdio.h> 
#include <stdlib.h> 
int main(int argc, char *argv[]) 
{ 
    int offset; 
    int ch1, ch2; 
    FILE *fh1, *fh2, *diffone=stdout, *file2=0; 


    if(argc<3) { 
      printf("need two file names\n"); return(1); 
    } 
    if(!(fh1 = fopen(argv[1], "r"))) { 
      printf("cannot open %s\n",argv[1]); return(2); 
    } 
    if(!(fh2 = fopen(argv[2], "r"))) { 
      printf("cannot open %s\n",argv[2]); return(3); 
    } 
    if(argc>3) { 
      if(!(diffone = fopen(argv[3], "w+"))) { 
       printf("cannot open %s\n",argv[3]); return(4); 
      } 
    } 
    if(argc>4) { 
      if(!(file2 = fopen(argv[4], "w+"))) { 
       printf("cannot open %s\n",argv[4]); return(4); 
      } 
    } 

    while((!feof(fh1)) && (!feof(fh2))) 
    { 
      ch1=ch2='-'; 
      if(!feof(fh1)) ch1 = getc(fh1); 
      if(!feof(fh2)) ch2 = getc(fh2); 
      if(ch1 != ch2) { 
       fprintf(diffone,"%c", ch1);//print to a console or file depending on the value of diffone 
       if (file2) fprintf(file2,"%c", ch1); 
      } 
     } 


    return 0; 
}