如何从文件中读取并在c中写入另一个

Question

我有一个这样的输入文件：

This is 1nd Line.
This is 2nd Line.
This 3rd Line.

我需要输出类似

的文件

OddLines.txt:

This is 1nd Line.
This 3rd Line.

EvenLines.txt:

This is 2nd Line.

这是我的代码。并没有按照我的意愿工作。

    char buf[256];
    int ch;
    int lines;
    lines = 1;

    FILE *myFile = fopen(argv[1], "r");

    if (myFile == NULL) {
        printf("Open error \n");
        exit(-1);
    }

    FILE *outFile = fopen("oddlines.txt", "w");
    FILE *outFile1 = fopen("evenlines.txt", "w");

    while (fgets(buf, sizeof(buf), myFile) != NULL) {
        if (ch == '\n')
            lines++;
        else
        if ((lines % 2) == 0)
            fputs(buf, outFile1);
        else
            fputs(buf, outFile);
    }
    fclose(myFile);
    fclose(outFile);
    fclose(outFile1);
}

Answer 1

if (ch == '\n')

这段代码没有意义。你想找到输入字符吗？如果是，您可以使用 strcspn 函数：

int pos = strcspn ( buf, "\n" );

lines 应该由 0 初始化，而不是 1:

    int lines = 0;
    while(fgets(buf, sizeof(buf),myFile))
    {
        lines++;
        int pos = strcspn ( buf, "\n" ); // find the enter character
        buf[pos] = ' '; // add space at the end of string
        buf[pos+1] = '[=12=]';
        if ((lines%2)==0) // if even
            fputs (buf,outFile1); 
        else               // if odd
            fputs (buf,outFile);
    }

您应该检查 fopen 函数：

FILE *myFile = fopen(argv[1], "r");
if(!myFile) {return -1;}

FILE *outFile = fopen("oddlines.txt", "w");
if(!outFile) {return -1;}
FILE *outFile1 = fopen("evenlines.txt", "w");
if(!outFile1) {return -1;}

以及命令行条件：

if(argc < 2 ) {
    printf("usage: %s <input_filename>", argv[0]);
    return-1;
}

完整代码：

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

int main(int argc, char const *argv[]) {

    char buf[256];
    int lines = 0;

    if(argc < 2 ) {
        printf("usage: %s <input_filename>", argv[0]);
        return-1;
    }

    FILE *myFile = fopen(argv[1], "r");
    if(!myFile) {return -1;}
    FILE *outFile = fopen("oddlines.txt", "w");
    if(!outFile) {return -1;}
    FILE *outFile1 = fopen("evenlines.txt", "w");
    if(!outFile1) {return -1;}

    while(fgets(buf, sizeof(buf),myFile)!=NULL)
    {
        lines++;
        int pos = strcspn ( buf, "\n" );
        buf[pos] = ' ';
        buf[pos+1] = '[=15=]';
        if ((lines%2)==0)
            fputs (buf,outFile1);
        else
            fputs (buf,outFile);
    }

    fclose(myFile);
    fclose(outFile);
    fclose(outFile1);
}

输入文件：

This is 1nd Line.
This is 2nd Line.
This is 3rd Line.
This is 4th Line.
This is 5th Line.
This is 6th Line.

输出文件：

$cat evenlines.txt

This is 2nd Line. This is 4th Line. This is 6th Line. 

$cat oddlines.txt

This is 1nd Line. This is 3rd Line. This is 5th Line.

Answer 2

if (ch == '\n')

问题出在这一行。

#include <stdio.h>
#include<string.h>
void main() 
{
    int line=1;
    char buf[256];

    FILE *fp, *fp_Odd, *fp_Even;
    fp=fopen("USERS.TXT", "r");

    fp_Odd=fopen("ODD.TXT", "a");
    fp_Even=fopen("EVEN.TXT", "a");

    if(fp == NULL)
    {
        printf("Open error \n");
        exit(-1);
    }

    while(fgets(buf, sizeof(buf), fp)!=NULL)
    {
        if(strcmp(buf, "\n")==0)
        line++;

        else if(line%2 != 0)
            fprintf(fp_Odd, "%s", buf);
        else
            fprintf(fp_Even, "%s", buf);

        line++;
    }
    fclose(fp);
}

您可以查看此代码。我已经进行了必要的更改。希望你明白。

Answer 3

不清楚您是希望输出文件包含输入文件中的行，还是必须连接这些行，去除换行符。

您的代码无法运行，因为测试 if (ch == '\n') 具有未定义的行为，因为 ch 未初始化。因此，行计数器未正确更新，所有行都进入其中一个文件。

计算行数实际上并不像计算循环迭代那么简单，因为输入文件中的某些行可能比 fgets() 使用的数组长度长。您应该在写入后更新行计数器，方法是测试刚刚写入的行是否实际包含换行符。

这是修改后的版本：

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

int main(int argc, char *argv[]) {
    char buf[256];
    int lines = 1;
    FILE *myFile, *outFile, *outFile1;

    if (argc < 2) {
        printf("Missing argument\n");
        return 1;
    }
    if ((myFile = fopen(argv[1], "r")) == NULL) {
        printf("Open error for %s\n", argv[1]);
        return 1;
    }
    if ((outFile = fopen("oddlines.txt", "w")) == NULL) {
        printf("Open error for %s\n", "oddlines.txt");
        return 1;
    }
    if ((outFile1 = fopen("evenlines.txt", "w")) == NULL) {
        printf("Open error for %s\n", "evenlines.txt");
        return 1;
    }

    while (fgets(buf, sizeof(buf), myFile) != NULL) {
        if (lines % 2 == 0)
            fputs(buf, outFile1);
        else
            fputs(buf, outFile);

        /* if a full line was read, increment the line number */
        if (strchr(buf, '\n')
            lines++;
    }
    fclose(myFile);
    fclose(outFile);
    fclose(outFile1);
    return 0;
}

这里是一个不使用fgets()的更简单的版本：

#include <stdio.h>

int main(int argc, char *argv[]) {
    int c, out;
    FILE *myFile, *outFile[2];

    if (argc < 2) {
        printf("Missing argument\n");
        return 1;
    }
    if ((myFile = fopen(argv[1], "r")) == NULL) {
        printf("Open error for %s\n", argv[1]);
        return 1;
    }
    if ((outFile[0] = fopen("oddlines.txt", "w")) == NULL) {
        printf("Open error for %s\n", "oddlines.txt");
        return 1;
    }
    if ((outFile[1] = fopen("evenlines.txt", "w")) == NULL) {
        printf("Open error for %s\n", "evenlines.txt");
        return 1;
    }

    out = 0; /* current output file is "oddlines.txt" */
    while ((c = getc(myFile)) != EOF) {
        putc(c, outFile[out]);
        if (c == '\n')
            out = 1 - out;  /* change current output file */
    }
    fclose(myFile);
    fclose(outFile[0]);
    fclose(outFile[1]);
    return 0;
}

如果您希望从第三个输出文件中去除元音，只需包含 <string.h>，打开该文件至 FILE *noVowelFile 并在 while 循环中添加一个测试：

    out = 0; /* current output file is "oddlines.txt" */
    while ((c = getc(myFile)) != EOF) {
        if (strchr("aeiouAEIOU", c) == NULL) {
            putc(c, noVowelFile);
        }
        putc(c, outFile[out]);
        if (c == '\n')
            out = 1 - out;  /* change current output file */
    }

如何从文件中读取并在c中写入另一个

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