C语言 文件读写到同一个文件？
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原文地址: http://stackoverflow.com/questions/5787867/
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File read write to same file?
提问by DaRk_f0x
I've managed to open a file and read while writing to another file with var=fopen(file,"r")/ "w"but even with r+ or w+ moded I can't open a file and alter its contents.
我设法打开一个文件并在使用var=fopen(file,"r")/写入另一个文件时读取，"w"但即使使用 r+ 或 w+ 模式，我也无法打开文件并更改其内容。
Imagine this:
想象一下：
int formatacao (char original[]){/*se a cadeia nao tiver escrita em maiusculas, esta fun?ao vai alteralas para tal*/
int val1;
FILE * original_open;
original_open = fopen (original,"r+");
if (original_open==0){
printf ("ficheiro %c 1.",original);
}
while ((val1=fgetc(original_open))!=EOF){
if (val1>='a'&&val1<='z'&&val1){
fputc(val1-32,original_open);
}
else
fputc(val1,original_open);
}
fclose (original_open);
return (0);
}
Code works, no errors, no warning, only problem is: it erases the contents on the file if I use it like this BUT this works:
代码有效，没有错误，没有警告，唯一的问题是：如果我像这样使用它，它会擦除文件中的内容，但这是有效的：
int main (){
int val1,val2,nr=0;
FILE* fp1;
FILE* fp2;
fp1=fopen ("DNAexample.txt","r");
fp2=fopen ("DNAexample1.txt","w");
if (fp1==0){
printf ("EPIC FAIL no 1.\n");
}
while ((val1=fgetc(fp1))!=EOF){
if (val1>='a'&&val1<='z'&&val1){
fputc(val1-32,fp2);
}
else
fputc(val1,fp2);
}
fclose (fp1);
fclose (fp2);
return (0);
}
Flawlessly! How can I open a file, read char by char and decide if I want to change the char or not?
完美无瑕！如何打开文件，逐个字符读取字符并决定是否要更改字符？
回答by pmg
You need to intervene a file positioning function between output and input unless EOF was found on input.
除非在输入上找到 EOF，否则您需要在输出和输入之间插入文件定位功能。
This works for me:
这对我有用：
#include <stdio.h>
int formatacao (char *original) {
int val1;
FILE *original_open;
int write_at, read_at;
original_open = fopen(original, "r+");
if (original_open == 0) {
printf("ficheiro %s\n", original);
}
write_at = read_at = 0;
while ((val1 = fgetc(original_open)) != EOF) {
read_at = ftell(original_open);
fseek(original_open, write_at, SEEK_SET);
if (('a' <= val1) && (val1 <= 'z')) {
fputc(val1 - 32, original_open);
} else {
fputc(val1, original_open);
}
write_at = ftell(original_open);
fseek(original_open, read_at, SEEK_SET);
}
fclose(original_open);
return (0);
}
int main(void) {
formatacao("5787867.txt");
return 0;
}
回答by anthares
Open the file with 'a+' option, in order to append to the file:
使用 'a+' 选项打开文件，以便附加到文件：
fopen ("DNAexample.txt","a+");
w+ will erase your file if exists or create new if the specified doesn't exist. a+ will open the existing file and you will be able to edit it.
w+ 将删除您的文件（如果存在）或创建新文件（如果指定的文件不存在）。a+ 将打开现有文件，您将能够对其进行编辑。
You can read more about file operations here: http://www.functionx.com/cppbcb/cfileprocessing.htm
您可以在此处阅读有关文件操作的更多信息：http: //www.functionx.com/cppbcb/cfileprocessing.htm
回答by AbhiRoczz...
Open file in append mode
以追加模式打开文件
original_open = fopen (original,"a+");
