Question

目前我能够（我认为）使用fopen打开文件。出于测试目的，我希望能够将文件的内容传递给输出文件，但是我没有得到预期的结果。这是一些代码：

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

int main(int argc, char* argv[]){ //practice on utilizing IO
char filepath[100];
char filepath2[100];
strcpy(filepath,"./");
strcpy(filepath,"./");
char typed[90];
char msg[1024];
FILE * new_file;
FILE * old_file;

// printf("Input file to be created\n");
printf("File to be opened as input: \n");
printf("--->");

fgets(typed,90,stdin); //read in file name
strtok(typed, "\n");
strcat(filepath,typed);
old_file =  fopen(filepath, "r");

printf("file to output to: \n");
fgets(filepath2,100, stdin);  
strtok(filepath2, "\n");
///attempt to create that file
new_file = fopen(filepath2,"w");
//printf("%s\n", msg);

}

感谢任何帮助。

Answer 1

在程序中打开文件句柄与在字处理器中打开文档略有不同。这更像是开书。要读或写，你必须用眼睛（消耗数据）或铅笔（产生数据）。

由于您打开了文件，因此需要从第一个文件中读取数据并将其写入第二个文件。类似的东西：

size_t nread;
do {
    nread = fread(msg, 1, 1024, old_file);
    fwrite(msg, 1, nread, new_file);
} while(nread != 0);

或者

int nread;
do {
    nread = fgets(msg, 1023, old_file);
    fputs(msg, new_file);
} while (nread > 0);

或者甚至一次只是一个字母。

int c;
while ( (c=fgetc(old_file)) != EOF) {
    fputc(c, new_file);
}

此外，您没有将“./”添加到第二个文件中。不确定这是否重要，但你是在第一个文件中做到的。

此外，您应该在new_file上使用fopen。 freopen本身不是错误的，但它很奇怪会让其他人（包括我）感到困惑。

freopen（）函数打开名称为指向的字符串的文件通过路径并将流指向的流与它相关联。该原始流（如果存在）已关闭。 mode参数仅用于就像在fopen（）函数中一样。 SRC：manpage

因此，它会根据您的意愿打开流，但它会在执行此操作时销毁stdout。所以你的程序不能再正常输出了。这可能并不重要，但似乎也没有任何真正的优势。

Answer 2

我创建了一个类似于你的小c文件，希望它可以帮助你更好地理解C中的i / o。

代码：

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

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

char fileNameOne[] = "test.txt";
char fileNameTwo[] = "new.txt";

FILE* oldFile;
FILE* newFile;

printf("The file being read from is: %s\n", fileNameOne);
//get a File pointer to the old file(file descriptor)
oldFile = fopen(fileNameOne, "r");

//get a File pointer to the new file(file descriptor)
//a+ is to open for read and writing and create if it doesnt exist
//if we did not specify a+, but w+ for writing, we would get an invalid file descriptor because the file does not exist
newFile = fopen(fileNameTwo, "a+");
if (newFile == 0) {
    printf("error opening file\n");
    exit(1);
}
//read everything from the old file into a buffer
char buffer[1024];

printf("Contents of old file:\n");
while (fread(buffer, 1, 1024, oldFile) != 0) {
    //if fread returns zero, and end of file has occured
     printf("%s", buffer);
     //directly write the contents of fileone to filetwo
     fwrite(buffer, 1, 1024, newFile);
}

printf("The file %s has been read and written to %s\n", fileNameOne, fileNameTwo);

printf("Verification: Contents of file two:\n");

//move the offset back to the beginning of the file
rewind(newFile);

while (fread(buffer, 1, 1024, newFile)!= 0) {
    printf("%s", buffer);
}

printf("\nEnd of file 2\n");
}

我在同一个目录中创建了一个名为test的文本文件，只是给它写了一些垃圾。这是输出。

输出：

The file being read from is: test.txt
Contents of old file:
Hi, my name is Jack!

HAHAHAH

YOU DON"T even know!


The file test.txt has been read and written to new.txt
Verification: Contents of file two:
Hi, my name is Jack!

HAHAHAH

YOU DON"T even know!



End of file 2

将输入文件传递给C中的输出文件？

2 个答案: