如何将字符串（由用户输入）与文件中一行的第一个单词进行比较？

这是一些可以满足您要求的代码。我认为它将帮助您更好地了解字符串函数的工作方式。注意-对于输入和文本文件的条件调整情况，我没有做很多假设，因此有很多代码可以从输入中删除空格，并检查匹配是否确实是“第一个单词”，而不是“第一个单词的第一部分”。因此，此代码不会将输入“ hello”与“ helloworld 123 234”行匹配，但将与“ helloworld 123 234”行匹配。还要注意，它目前区分大小写。

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

int main(void) {
  char buf[100];     // declare space for the input string
  FILE *fp;          // pointer to the text file
  char fileBuf[256]; // space to keep a line from the file
  int ii, ll;

  printf("give a word to check:\n");
  fgets(buf, 100, stdin);    // fgets prevents you reading in a string longer than buffer
  printf("you entered: %s\n", buf);  // check we read correctly

  // see (for debug) if there are any odd characters:
  printf("In hex, that is ");
  ll = strlen(buf);
  for(ii = 0; ii < ll; ii++) printf("%2X ", buf[ii]);
  printf("\n");

  // probably see a carriage return - depends on OS. Get rid of it!
  // note I could have used the result that ii is strlen(but) but 
  // that makes the code harder to understand
  for(ii = strlen(buf) - 1; ii >=0; ii--) {
    if (isspace(buf[ii])) buf[ii]='\0';
  }

  // open the file:
  if((fp=fopen("myFile.txt", "r"))==NULL) {
    printf("cannot open file!\n");
    return 0;
  }

  while( fgets(fileBuf, 256, fp) ) {   // read in one line at a time until eof
    printf("line read: %s", fileBuf);  // show we read it correctly
  // find whitespace: we need to keep only the first word.
    ii = 0;
    while(!isspace(fileBuf[ii]) && ii < 255) ii++;
  // now compare input string with first word from input file:
  if (strlen(buf)==ii && strstr(fileBuf, buf) == fileBuf) {
        printf("found a matching line: %s\n", fileBuf);
        break;
    }
  }
  // when you get here, fileBuf will contain the line you are interested in
  // the second and third word of the line are what you are really after.
}