命令行参数和使用C读取文件/打印文本 [英] Command line arguments and read file/print text in C

问题描述

我想用命令行参数的工作和解析C.一个文本文件基本上，我希望能够把两个数字一样，1和4，并把它读取文本文件的一列，然后打印出来到标准输出。我希望能够做这样的事情借此：

I am trying to work with command line arguments and parsing a text file in C. Basically I want to be able to put in two numbers, like, 1 and 4 and have it read a column of a text file then print it to stdout. I want to be able to do something like take this:

PID   TTY        TIME     CMD
449   ttys000    0:00.35 -bash
1129  ttys001    0:00.35 -bash
25605 ttys001    0:00.15  vi prog.c
6132  ttys002    0:00.11 -bash
6208  ttys002    0:00.03  vi test

和做的：

./your_prog 1 4 < data.txt 

PID CMD
449 bash
1129 -bash
25605 vi
6132 -bash 
6208 vi 

所以我需要输入我想打印出来，在重定向的data.txt文件并把它处理文件和打印像这样的列。

So I need to enter the the columns i want to print out, redirect the file in "data.txt" and have it process the file and print like so.

到目前为止，我有这对我的code：

So far I have this for my code:

 #include <stdio.h>
 int main(int argc, char **argv){
//int row = argc[0];
//int col = argc[1];
//if number entered is less than one, re-enter

int i;
for (i = 0; i < argc; i++) {
  printf("argv[%d] = %s\n", i, argv[i]);
}
if(argc < 1){
  fprintf(stderr, "Enter a valid input");

  //quit
  return 1;
} 
else{   
  char ch[256];
  //ch[255] = '\0';

    while(fgets(ch, 256, stdin) != NULL){
      printf("%s", ch);
    }
  } 
  return 1;
}

但我不知道如果我是正确的轨道上，并很困惑，下一步该怎么做。我是新来的C，所以我道歉，如果这是一个简单的问题。

but am not sure if I am on the correct track and am confused as to what to do next. I am new to C, so I apologize if this is an easy question.

推荐答案

为您开始，这可以提高你收集的命令行信息的方式。注意第一个参数的argv [0] 是可执行文件本身的名称。熊上面记的意见，我也没有提高任何进一步。语法是的progname名COL1 COL2

To get you started, this improves the way you gather the command line information. Note the first argument argv[0] is the name of the executable itself. Bear in mind comments above, I haven't improved any further. Syntax is progname filename col1 col2

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

void fatal(char *msg) {
    printf("%s\n", msg);
    exit (1);
}

int main(int argc, char*argv[])
{
    int col1, col2;
    FILE *fp;
    char ch[256];

    if(argc < 4)
        fatal("Need three arguments");

    if (sscanf(argv[2], "%d", &col1) != 1)
        fatal("Argument 1 error");

    if (sscanf(argv[3], "%d", &col2) != 1)
        fatal("Argument 2 error");

    printf("Read columns %d and %d from file %s\n", col1, col2, argv[1]);
    if ((fp = fopen(argv[1], "r")) == NULL)
        fatal("Unable to open file");

    // process the file
    while (fgets(ch, 256, fp) != NULL) {
        printf("%s", ch);
    }
    fclose(fp);
    return 0;
}

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