# std::fwrite

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< cpp‎ | io‎ | c

Defined in header `<cstdio>` |  |
std::size_t fwrite( const void* buffer, std::size_t size, std::size_t count, std::FILE* stream ); |  |

Writes up to `count` binary objects from the given array `buffer` to the output stream `stream`. The objects are written as if by reinterpreting each object as an array of unsigned char and calling std::fputc `size` times for each object to write those unsigned chars into `stream`, in order. The file position indicator for the stream is advanced by the number of characters written.

If the objects are not TriviallyCopyable, the behavior is undefined.

If an error occurs, the resulting value of the file position indicator for the stream is indeterminate.

### Parameters

buffer | - | pointer to the first object object in the array to be written
size | - | size of each object
count | - | the number of the objects to be written
stream | - | output file stream to write to

### Return value

Number of objects written successfully, which may be less than `count` if an error occurred.

If `size` or `count` is zero, `fwrite` returns zero and performs no other action.

### Example

Run this code

    #include <cstdio>
    #include <vector>
    #include <array>

    int main ()
    {
        // write buffer to file
        if(std::FILE* f1 = std::fopen("file.bin", "wb")) {
            std::array<int, 3> v = {42, -1, 7}; // underlying storage of std::array is an array
            std::fwrite(v.data(), sizeof v[0], v.size(), f1);
            std::fclose(f1);
        }

        // read the same data and print it to the standard output
        if(std::FILE *f2 = std::fopen("file.bin", "rb")) {
            std::vector<int> rbuf(10); // underlying storage of std::vector is also an array
            std::size_t sz = std::fread(rbuf.data(), sizeof rbuf[0], rbuf.size(), f2);
            std::fclose(f2);
            for(std::size_t n = 0; n < sz; ++n) {
                std::printf("%d\n", rbuf[n]);
            }
        }
    }

Output:

    42
    -1
    7

### See also

printf fprintf sprintf snprintf (C++11) | prints formatted output to stdout, a file stream or a buffer (function)
fputs | writes a character string to a file stream (function)
fread | reads from a file (function)

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