Strcmp未比较argv中的字符串

**更新26/10->首先感谢你们的帮助，我现在离你们越来越近了，我需要更多的工作和学习，但我真的很感谢你们对我的帮助：-）

---

仍然不知道为什么input.txt文件中的第一个“rain”字没有从strcmp获得正输出，从cmd我可以看到“问题在于

str

缓冲区末尾的

\n

fgets

在它读取的行的末尾添加

\n

，您需要在比较之前除去它

这就是您需要的：

  while (fgets(str, 60, fp) != NULL) {

    /* remove \n from at the end of the str buffer*/    
    char *pos;
    if ((pos = strchr(str, '\n')) != NULL)
      *pos = '\0';

    /* print str enclosed in <> so we can see what str actually contains */
    printf("Inside the loop, got the string: <%s>\n", str);

    if (strcmp(compare, str) == 0) {
      printf("Found it! %s\n", str);
      fprintf(fo, "%s\n", replace);
    }
    else {
      fprintf(fo, "%s\n", str);
    }
  }

while（fgets（str，60，fp）！=NULL）{
/*从str缓冲区结尾处删除\n*/
char*pos；
如果（（pos=strhr（str，'\n'））！=NULL）
*pos='\0'；
/*打印包含在中的str，以便我们可以看到str实际包含的内容*/
printf（“在循环中，得到字符串：\n”，str）；
if（strcmp（比较，str）==0）{
printf（“找到了！%s\n”，str）；
fprintf（fo，“%s\n”，替换）；
}
否则{
fprintf（fo，“%s\n”，str）；
}
}

---

请查看代码中的注释以获取解释。

您的方法失败，因为从输入文件读取的行包含一个使比较返回非零的尾随换行符

'\n'

在与搜索字符串进行比较之前，可以去掉换行符

请注意，还有其他问题：

• 您应该通过测试

  argc>4

  来验证是否传递了足够的命令行参数
• 无需在更新模式下打开输出文件，

  “w+”

  ，

  “w”

  更简单、更好
• 60字节对于行数组来说有点小，将正确处理的最长行限制为58字节

以下是一个改进的版本：

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

int main(int argc, char **argv) {
    FILE *fp, *fo;
    char *compare, *replace;
    char line[256];

    if (argc <= 4) {
        printf("missing command line arguments\n");
        return 1;
    }
    fp = fopen(argv[1], "r");
    if (fp == NULL) {
        perror("Error opening input file");
        return 1;
    }
    compare = argv[2];
    fo = fopen(argv[3], "w");
    if (fo == NULL) {
        perror("Error opening output file");
        return 1;
    }
    replace = argv[4];

    while (fgets(line, sizeof line, fp) != NULL) {
        line[strcspn(line, "\n")] = '\0';
        if (strcmp(line, compare) == 0) {
            printf("fount it!);
            fprintf(fo, "%s\n", replace);
        } else {
            fprintf(fo, "%s\n", line);
        }
    }
    fclose(fp);
    fclose(fo);

    return 0;
}

---

从

man fgets

char*fgets（char*s、int大小、文件*流）

fgets（）从流中最多读入一个小于大小的字符，并将它们存储到缓冲区中 由s。EOF或换行符后，读取停止如果读取换行符，则将其存储到缓冲区。a 终止空字节（'\0'）存储在缓冲区中最后一个字符之后

因此，您需要从缓冲区

s

中删除换行符，类似于：

c[strlen(c) - 1] = 0 when c[strlen(c) - 1] == '\n'

读.c

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

/**
* How to compile program:
*    gcc read.c -o read
*
* How to run the program: 
*      .> ./read input.txt rainy output.txt sunny
* (On Windows MinGW compiler, simply: 
*      .> read input.txt rainy output.txt sunny - without ./)
*
*/
int main (int argc, char **argv) {
   FILE *fp, *fo;
   char *compare, *replace;
   char line[246];

   if (argc <= 4){
      printf(">Missing arguments on the command line.\n");
      printf(">Be sure you run the program as\n\"./read input.txt compare outout.txt replace\"\n\n");
   }

   /* Opening files for reading */
   fp = fopen(argv[1] , "r");
   if(fp == NULL){
      perror("Error opening input file");
      return 1;
   }
   compare = argv[2];

   fo = fopen(argv[3], "w");
   if(fo == NULL){
      perror("Error opening output file");
      return 1; 
   }
   replace = argv[4];

   while( fgets (line, (sizeof line), fp)!=NULL ) {
      line[strcspn(line, "\n")] = 0;
       if(strcmp(compare, line) == 0){
         printf("Found it! %s \n", line);
         fprintf(fo, "%s\n", replace);
      }
      else{
         fprintf(fo, "%s\n", line);
      } 
   }
   fclose(fp);
   fclose(fo);
   return 0;
}

/* 
Important info

strcspn :: 
Locate first occurrence of character in string, 
after locating the first occurrence of \n, replaces it by 0.


Sources::
https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input/28462221#28462221

Used to debug:
.>printf("1st: Reads input.txt, removes '\\n' from fgets, and prints it \n");
.>printf("2nd: Compares each line with 'rainy' \n");


.>printf("<%s>\n", line);

*/

---

不检查

fo

是否为空。并且不检查

argc

是否小于5。请提供一个最小的

input.txt

文件，以便重现问题。这种方法仅在输入文件中每行文本有一个单词时有效。但是您忽略了

fgets

在输入字符串的末尾保留了换行符。请看标题上的注释：你应该找一个更好的。你让它听起来好像

strcmp（）

无法正常工作，但事实并非如此。。。此外，作为一名程序员，您需要提供一个示例文件和一个示例输入，以及程序的预期和实际输出。@JessicaPereira可能这不是问题所在，但无论如何您都应该检查。用户可以使用无效参数调用您的程序，并且可能由于任何原因无法创建输出文件。“可能它在命令行上有额外的空间，我不知道”——为什么不使用定义的分隔符打印字符串以查找，例如

printf（“\n”，str）

？或者使用一个调试器，它将为您比较的strigs提供C表示？这样的事情很容易发现。

./read2 input.txt rain output.txt sun 

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

int main(int argc, char **argv) {
    FILE *fp, *fo;
    char str[60];

    //char* token;
    /* opening file for reading */
    fp = fopen(argv[1], "r");
    char *compare = argv[2];

    fo = fopen(argv[3], "w+");
    char *replace = argv[4];

    if (fp == NULL) {
        perror("Error opening file");
        return(-1);
    }

    //printf("We are going to compare %s\n", compare);

    //printf("We are going to replace it with %s\n", replace);

    while (fgets(str, 60, fp) != NULL) {
        /* writing content to stdout */
        //Take the \n out 
        //token = strtok(str, "\n");

        printf("Inside the loop, got the string: %s\n", str);
        if (strcmp(compare, str) == 0) {
            //puts(str);
            printf("Found it! %s \n", str);

            fprintf(fo, "%s", replace);
        } else {
            fprintf(fo, "%s", str);
        }
    }
    fclose(fp);

    return(0);
}

Maria
rain
manel
Bla bla
rain 

  while (fgets(str, 60, fp) != NULL) {

    /* remove \n from at the end of the str buffer*/    
    char *pos;
    if ((pos = strchr(str, '\n')) != NULL)
      *pos = '\0';

    /* print str enclosed in <> so we can see what str actually contains */
    printf("Inside the loop, got the string: <%s>\n", str);

    if (strcmp(compare, str) == 0) {
      printf("Found it! %s\n", str);
      fprintf(fo, "%s\n", replace);
    }
    else {
      fprintf(fo, "%s\n", str);
    }
  }

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

int main(int argc, char **argv) {
    FILE *fp, *fo;
    char *compare, *replace;
    char line[256];

    if (argc <= 4) {
        printf("missing command line arguments\n");
        return 1;
    }
    fp = fopen(argv[1], "r");
    if (fp == NULL) {
        perror("Error opening input file");
        return 1;
    }
    compare = argv[2];
    fo = fopen(argv[3], "w");
    if (fo == NULL) {
        perror("Error opening output file");
        return 1;
    }
    replace = argv[4];

    while (fgets(line, sizeof line, fp) != NULL) {
        line[strcspn(line, "\n")] = '\0';
        if (strcmp(line, compare) == 0) {
            printf("fount it!);
            fprintf(fo, "%s\n", replace);
        } else {
            fprintf(fo, "%s\n", line);
        }
    }
    fclose(fp);
    fclose(fo);

    return 0;
}

int c;
int pos = 0;
int cmplen = strlen(compare);
for (;;) {
    c = getc(fp);
    if (c == '\n' || c == EOF) {
        if (pos == cmplen) {
            fprintf(fo, "%s", replace);
        } else
        if (pos > 0) {
            fprintf(fo, "%*s", pos, compare);
        }
        pos = 0;
        if (c == EOF)
            break;
    } else {
        if (pos >= 0) {
            if (compare[pos] == (char)c) {
                pos++;
                continue;
            }
            if (pos > 0) {
                fprintf(fo, "%*s", pos, compare);
            }
            pos = -1;
        }
    }
    putc(c, fo);
}

c[strlen(c) - 1] = 0 when c[strlen(c) - 1] == '\n'

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

/**
* How to compile program:
*    gcc read.c -o read
*
* How to run the program: 
*      .> ./read input.txt rainy output.txt sunny
* (On Windows MinGW compiler, simply: 
*      .> read input.txt rainy output.txt sunny - without ./)
*
*/
int main (int argc, char **argv) {
   FILE *fp, *fo;
   char *compare, *replace;
   char line[246];

   if (argc <= 4){
      printf(">Missing arguments on the command line.\n");
      printf(">Be sure you run the program as\n\"./read input.txt compare outout.txt replace\"\n\n");
   }

   /* Opening files for reading */
   fp = fopen(argv[1] , "r");
   if(fp == NULL){
      perror("Error opening input file");
      return 1;
   }
   compare = argv[2];

   fo = fopen(argv[3], "w");
   if(fo == NULL){
      perror("Error opening output file");
      return 1; 
   }
   replace = argv[4];

   while( fgets (line, (sizeof line), fp)!=NULL ) {
      line[strcspn(line, "\n")] = 0;
       if(strcmp(compare, line) == 0){
         printf("Found it! %s \n", line);
         fprintf(fo, "%s\n", replace);
      }
      else{
         fprintf(fo, "%s\n", line);
      } 
   }
   fclose(fp);
   fclose(fo);
   return 0;
}

/* 
Important info

strcspn :: 
Locate first occurrence of character in string, 
after locating the first occurrence of \n, replaces it by 0.


Sources::
https://stackoverflow.com/questions/2693776/removing-trailing-newline-character-from-fgets-input/28462221#28462221

Used to debug:
.>printf("1st: Reads input.txt, removes '\\n' from fgets, and prints it \n");
.>printf("2nd: Compares each line with 'rainy' \n");


.>printf("<%s>\n", line);

*/

cloudy
rainy
chilly
rainy
rainy