C从文件中删除最后n个字符 [英] C Delete last n characters from file

问题描述

我需要使用C代码从文件中删除最后n个字符.一开始，我试图使用'\ b'，但它返回了Segmentation Fault.我在此处和

I need to delete the last n characters from a file using C code. At fist I was trying to use '\b', but it returns a Segmentation Fault. I have seen interesting answers to similar questions here and here, but I would prefer to use mmap function to do this, if it's possible. I know it could be simpler to truncate the file by creating a temp file, and writing chars to temp until some offset of the original file. The problem is I don't seem to understand how to use mmap function to do this, can't see what parameters I need to pass to that function, specially address, length and offset. From what I've read, I should use MAP_SHARED in flags and PROT_READ|PROT_WRITE in protect.

函数定义为:

void * mmap (void *address, size_t length, int protect, int flags, int filedes, off_t offset)

这是我的主要爱好:

int main(int argc, char * argv[])
{
    FILE * InputFile;
    off_t position;
        int charsToDelete;

    if ((InputFile = fopen(argv[1],"r+")) == NULL)
    {
            printf("tdes: file not found: %s\n",argv[1]);
    }
    else
    {
                charsToDelete = 5;
        fseeko(InputFile,-charsToDelete,SEEK_END);
        position = ftello(InputFile);
        printf("Pos: %d\n",(int)position);
        int i;
        //for(i = 0;i < charsToDelete;i++)
        //{
        //  putc(InputFile,'\b');
        //}
    }
    fclose(InputFile);
    return 0;
}

推荐答案

为什么不使用:

   #include <unistd.h>
   #include <sys/types.h>

   int truncate(const char *path, off_t length);
   int ftruncate(int fd, off_t length);

例如:

    charsToDelete = 5;
    fseeko(InputFile,-charsToDelete,SEEK_END);
    position = ftello(InputFile);
    ftruncate(fileno(InputFile), position);

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