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：

这是第 1 行。 这是第 2 行。 这第 3 行。

我需要输出类似的文件

OddLines.txt：

这是第 1 行。 这第 3 行。

EvenLines.txt：

这是第 2 行。

这是我的代码。并没有按我的意愿工作。

    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

不清楚您是否希望输出文件包含输入文件中的行，或者这些行是否必须连接起来，去掉换行符。

您的代码不起作用，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的迭代次数那么简单，因为输入文件中的某些行可能比fgets() 使用的数组长度长。您应该在写入后通过测试刚刚写入的行是否实际上包含换行符来更新行计数器。

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;
}

这里有一个更简单的版本，不使用fgets()：

#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;
}

如果您想从第三个输出文件中去除元音，只需包含<string.h>，将该文件打开到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 */
    }

Answer 2

if (ch == '\n')

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

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

lines 应该由 0 而不是 1 初始化：

    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] = '\0';
        if ((lines%2)==0) // if even
            fputs (buf,outFile1); 
        else               // if odd
            fputs (buf,outFile);
    }

你应该检查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;}

以及命令行的条件：

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] = '\0';
        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 3

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);
}

您可以检查此代码。我已经进行了必要的更改。希望你能理解。